Rebecca Williams is Fellow and Tutor in Law at Pembroke College, Oxford University.

The book casts a fresh light on the relationship between ultra vires conduct of public bodies and the reason underlying rights to restitution in such circumstances. It is a well-written and valuable contribution to both restitution and public law scholarship. This work is likely to be very valuable not only to academics but also to practitioners (tax and non-tax) advising on restitution claims involving national or EU public bodies. Rafal Zakrzewski British Tax Review No. 3, 2012 Williams...presents a clear and well-argued case for a public law of unjust enrichment. Her approach is thoughtful and considered covering key cases in English, French and EU law, and focuses on an area of law of particular topicality...While her argument does, as she states, remain normative, lacking case law support, she nevertheless provides a lucid and well-researched argument for reform. Williams must thus be praised for drawing together and critically appraising the leading cases in this field and for providing valuable insight into this developing area of the law. Paula Giliker European Law Review Volume 36, 2011 Unjust Enrichment and Public Law is an important contribution to this topical subject. The discussion of English law is comprehensive and well argued, and will interest both public and private lawyers. Unjust Enrichment and Public Law is a well-written and well-presented book, which does much to advance our understanding of this difficult area of law. It deserves the attention of lawyers across the public/private divide. Paul S. Davies The Law Quarterly Review Volume 127, July 2011

• Part 1 Unjust Enrichment and Public Law in England and Wales 1-Definitions and Controversies 'RESTITUTION' OR 'UNJUST ENRICHMENT' Using the Map The Criteria for a Claim in 'Autonomous' Unjust Enrichment 'PUBLIC BODIES' AND 'PUBLIC LAW' CONCLUSION 2-Woolwich and the Creation of the Public Law Reason for Restitution THE FACTS THE BACKGROUND TO THE CLAIM A WHOLLY PRIVATE APPROACH? POTENTIAL UNJUST FACTORS AVAILABLE TO THE WOOLWICH Duress or Colore Officii Inequality No Consideration Failure of Consideration Mistake of Law TWO NEW OPTIONS FOR RECOVERY WHAT IS THE WOOLWICH UNJUST FACTOR? Illegality Incapacity Absence or failure of basis Inequality A WHOLLY PUBLIC APPROACH: COULD RESTITUTION SIMPLY BE A RESPONSE TO A PUBLIC LAW EVENT? THE SOLUTION: A HYBRID APPROACH 3-The Scope of the Public Law Reason for Restitution THE SCOPE OF THE PUBLIC LAW REASON FOR RESTITUTION: EIGHT KEY QUESTIONS Need There Have Been a Demand for the Public Law Reason for Restitution to Operate? Need There Have Been a Protest for the Public Law Reason for Restitution to Operate? To What Extent is the Public Law Reason for Restitution Overridden by Statute? What Exactly Does the Claimant Recover? Is it Always Necessary to Bring Two Separate Cases, One Action for Judicial Review and One Private Law Claim? Over What Subject Matter does the Public Law Reason for Restitution Extend? What Sort of Invalidity Triggers this Reason for Restitution? Which Kinds of Body Will Give Rise to this Reason for Restitution? THE SCOPE OF THE PUBLIC LAW UNJUST FACTOR: RESTITUTION FOR PUBLIC BODIES The 'Swaps' Cases 4-A Hierarchy of Reasons for Restitution THE ADVANTAGES OF THE PUBLIC LAW REASON FOR RESTITUTION OVER THE PRIVATE LAW UNJUST FACTORS REASONS FOR RESTITUTION AND TIME LIMITS: IS A HIERARCHY POSSIBLE? Deutsche Morgan Grenfell v IRC FURTHER ARGUMENTS AGAINST THE HIERARCHY Does Mistake Provide a Broader Ground of Recovery than the Public Law Reason for Restitution? HOW WIDE ARE THE EFFECTS OF THE PUBLIC LAW REASON FOR RESTITUTION? How Wide is the Finding of Ultra Vires? How Far does a Claim in Unjust Enrichment Extend into Consequential Loss? EVIDENCE FOR THE HIERARCHY AND THE ISSUE OF 'CLOSED' SWAPS CONCLUSION 5-Defences WHAT GENERAL IMPLICATIONS DOES THE HYBRID NATURE OF THE REASON FOR RESTITUTION HAVE FOR DEFENCES? TIME LIMITS PRIVATE LAW DEFENCES Change of Position Estoppel Bona Fide Purchase Impossibility of Counter-Restitution Submission to an Honest Claim Ultra Vires Passing On SPECIAL DEFENCES IN PUBLIC LAW UNJUST FACTOR CASES Fiscal Disruption The Law Commission's 'Special' Defence of Exhaustion of the Statutory Mechanism Prospective Overruling CONCLUSIONS AND FURTHER IMPLICATIONS Part 1 Conclusions and further implications Part 2 Unjust Enrichment and Public Law in France 6-Public Body Unjust Enrichment Claims in France; Lessons for England and Wales THE PUBLIC/PRIVATE DIVIDE IN FRANCE THE FRENCH LAW OF UNJUST ENRICHMENT Enrichissement Sans Cause Repetition de l'indu Gestion d'affaires ENRICHMENT WITHOUT CAUSE AND PUBLIC BODIES Quasi-Contracts are Automatically Adjusted in their Application to Public Bodies If Courts Have to Choose Between Two Events, Both of which are Actually Relevant to the Basis of the Claim, Some Courts Will Choose One, and Others the Other As well as Adjusting its Quasi-Contracts to Take Account of Public Bodies, French Law Also Distinguishes between Public Law Rules and Public Law Procedure, so that even within the Private Procedure Adjustments can be Made to Take Account of the Public Nature of one of the Parties to the Claim The 'Absence of Cause' Approach does not Necessarily Provide a Better Solution for Public Body Enrichment Cases The Need to Accommodate Public Bodies in Private Claims has a Tendency to Change the Rules of Private Law Itself CONCLUSION Part 3 Unjust Enrichment and Public Law in the European Union 7-Unjust Enrichment and the EU Institutions AN EU LAW OF UNJUST ENRICHMENT? UNJUST ENRICHMENT AS A GENERAL PRINCIPLE OF EU LAW Staff Cases Annulment Cases Three Party Cases UNJUST ENRICHMENT: ONLY A 'GENERAL PRINCIPLE' OF EU LAW CONCLUSION 8-Unjust Enrichment in National and European Law, and the 'Remedies' Jurisprudence of the ECJ HISTORICAL DEVELOPMENT OF THE RELEVANT EUROPEAN UNION LAW THE MEMBER STATE/EU DIVIDE: REMEDIES IN NATIONAL COURTS FOR BREACH OF EUROPEAN LAW The Principles of National Procedural Autonomy, Equivalence and Effectiveness, and the Three Phases of the ECJ's Case Law UNJUST ENRICHMENT AND ULTRA VIRES IN NATIONAL AND EU LAW; TWO DIFFERENT MODELS FOR ANALYSING THE DIVISION OF LABOUR BETWEEN THE MEMBER STATES AND THE EU Two important factors against Model 2 Cases in which a Member State or a National Intervention Agency Levies Money in Contravention of EU Law Cases in which an NIA or the EU Pays Out Money in Breach of EU Law which it then Seeks to Recover IS THERE AN EU LAW 'EVENT' OF ULTRA VIRES IN CASES INVOLVING BOTH EU AND NATIONAL LAW? CONCLUSION-THE IMPACT OF EU LAW ON NATIONAL UNJUST ENRICHMENT CLAIMS INVOLVING PUBLIC BODIES

Rebecca Williams is Fellow and Tutor in Law at Pembroke College, Oxford University.

The book casts a fresh light on the relationship between ultra vires conduct of public bodies and the reason underlying rights to restitution in such circumstances. It is a well-written and valuable contribution to both restitution and public law scholarship. This work is likely to be very valuable not only to academics but also to practitioners (tax and non-tax) advising on restitution claims involving national or EU public bodies. Rafal Zakrzewski British Tax Review No. 3, 2012 Williams...presents a clear and well-argued case for a public law of unjust enrichment. Her approach is thoughtful and considered covering key cases in English, French and EU law, and focuses on an area of law of particular topicality...While her argument does, as she states, remain normative, lacking case law support, she nevertheless provides a lucid and well-researched argument for reform. Williams must thus be praised for drawing together and critically appraising the leading cases in this field and for providing valuable insight into this developing area of the law. Paula Giliker European Law Review Volume 36, 2011 Unjust Enrichment and Public Law is an important contribution to this topical subject. The discussion of English law is comprehensive and well argued, and will interest both public and private lawyers. Unjust Enrichment and Public Law is a well-written and well-presented book, which does much to advance our understanding of this difficult area of law. It deserves the attention of lawyers across the public/private divide. Paul S. Davies The Law Quarterly Review Volume 127, July 2011

• Part 1 Unjust Enrichment and Public Law in England and Wales 1-Definitions and Controversies 'RESTITUTION' OR 'UNJUST ENRICHMENT' Using the Map The Criteria for a Claim in 'Autonomous' Unjust Enrichment 'PUBLIC BODIES' AND 'PUBLIC LAW' CONCLUSION 2-Woolwich and the Creation of the Public Law Reason for Restitution THE FACTS THE BACKGROUND TO THE CLAIM A WHOLLY PRIVATE APPROACH? POTENTIAL UNJUST FACTORS AVAILABLE TO THE WOOLWICH Duress or Colore Officii Inequality No Consideration Failure of Consideration Mistake of Law TWO NEW OPTIONS FOR RECOVERY WHAT IS THE WOOLWICH UNJUST FACTOR? Illegality Incapacity Absence or failure of basis Inequality A WHOLLY PUBLIC APPROACH: COULD RESTITUTION SIMPLY BE A RESPONSE TO A PUBLIC LAW EVENT? THE SOLUTION: A HYBRID APPROACH 3-The Scope of the Public Law Reason for Restitution THE SCOPE OF THE PUBLIC LAW REASON FOR RESTITUTION: EIGHT KEY QUESTIONS Need There Have Been a Demand for the Public Law Reason for Restitution to Operate? Need There Have Been a Protest for the Public Law Reason for Restitution to Operate? To What Extent is the Public Law Reason for Restitution Overridden by Statute? What Exactly Does the Claimant Recover? Is it Always Necessary to Bring Two Separate Cases, One Action for Judicial Review and One Private Law Claim? Over What Subject Matter does the Public Law Reason for Restitution Extend? What Sort of Invalidity Triggers this Reason for Restitution? Which Kinds of Body Will Give Rise to this Reason for Restitution? THE SCOPE OF THE PUBLIC LAW UNJUST FACTOR: RESTITUTION FOR PUBLIC BODIES The 'Swaps' Cases 4-A Hierarchy of Reasons for Restitution THE ADVANTAGES OF THE PUBLIC LAW REASON FOR RESTITUTION OVER THE PRIVATE LAW UNJUST FACTORS REASONS FOR RESTITUTION AND TIME LIMITS: IS A HIERARCHY POSSIBLE? Deutsche Morgan Grenfell v IRC FURTHER ARGUMENTS AGAINST THE HIERARCHY Does Mistake Provide a Broader Ground of Recovery than the Public Law Reason for Restitution? HOW WIDE ARE THE EFFECTS OF THE PUBLIC LAW REASON FOR RESTITUTION? How Wide is the Finding of Ultra Vires? How Far does a Claim in Unjust Enrichment Extend into Consequential Loss? EVIDENCE FOR THE HIERARCHY AND THE ISSUE OF 'CLOSED' SWAPS CONCLUSION 5-Defences WHAT GENERAL IMPLICATIONS DOES THE HYBRID NATURE OF THE REASON FOR RESTITUTION HAVE FOR DEFENCES? TIME LIMITS PRIVATE LAW DEFENCES Change of Position Estoppel Bona Fide Purchase Impossibility of Counter-Restitution Submission to an Honest Claim Ultra Vires Passing On SPECIAL DEFENCES IN PUBLIC LAW UNJUST FACTOR CASES Fiscal Disruption The Law Commission's 'Special' Defence of Exhaustion of the Statutory Mechanism Prospective Overruling CONCLUSIONS AND FURTHER IMPLICATIONS Part 1 Conclusions and further implications Part 2 Unjust Enrichment and Public Law in France 6-Public Body Unjust Enrichment Claims in France; Lessons for England and Wales THE PUBLIC/PRIVATE DIVIDE IN FRANCE THE FRENCH LAW OF UNJUST ENRICHMENT Enrichissement Sans Cause Repetition de l'indu Gestion d'affaires ENRICHMENT WITHOUT CAUSE AND PUBLIC BODIES Quasi-Contracts are Automatically Adjusted in their Application to Public Bodies If Courts Have to Choose Between Two Events, Both of which are Actually Relevant to the Basis of the Claim, Some Courts Will Choose One, and Others the Other As well as Adjusting its Quasi-Contracts to Take Account of Public Bodies, French Law Also Distinguishes between Public Law Rules and Public Law Procedure, so that even within the Private Procedure Adjustments can be Made to Take Account of the Public Nature of one of the Parties to the Claim The 'Absence of Cause' Approach does not Necessarily Provide a Better Solution for Public Body Enrichment Cases The Need to Accommodate Public Bodies in Private Claims has a Tendency to Change the Rules of Private Law Itself CONCLUSION Part 3 Unjust Enrichment and Public Law in the European Union 7-Unjust Enrichment and the EU Institutions AN EU LAW OF UNJUST ENRICHMENT? UNJUST ENRICHMENT AS A GENERAL PRINCIPLE OF EU LAW Staff Cases Annulment Cases Three Party Cases UNJUST ENRICHMENT: ONLY A 'GENERAL PRINCIPLE' OF EU LAW CONCLUSION 8-Unjust Enrichment in National and European Law, and the 'Remedies' Jurisprudence of the ECJ HISTORICAL DEVELOPMENT OF THE RELEVANT EUROPEAN UNION LAW THE MEMBER STATE/EU DIVIDE: REMEDIES IN NATIONAL COURTS FOR BREACH OF EUROPEAN LAW The Principles of National Procedural Autonomy, Equivalence and Effectiveness, and the Three Phases of the ECJ's Case Law UNJUST ENRICHMENT AND ULTRA VIRES IN NATIONAL AND EU LAW; TWO DIFFERENT MODELS FOR ANALYSING THE DIVISION OF LABOUR BETWEEN THE MEMBER STATES AND THE EU Two important factors against Model 2 Cases in which a Member State or a National Intervention Agency Levies Money in Contravention of EU Law Cases in which an NIA or the EU Pays Out Money in Breach of EU Law which it then Seeks to Recover IS THERE AN EU LAW 'EVENT' OF ULTRA VIRES IN CASES INVOLVING BOTH EU AND NATIONAL LAW? CONCLUSION-THE IMPACT OF EU LAW ON NATIONAL UNJUST ENRICHMENT CLAIMS INVOLVING PUBLIC BODIES

Rebecca Williams is Fellow and Tutor in Law at Pembroke College, Oxford University.

The book casts a fresh light on the relationship between ultra vires conduct of public bodies and the reason underlying rights to restitution in such circumstances. It is a well-written and valuable contribution to both restitution and public law scholarship. This work is likely to be very valuable not only to academics but also to practitioners (tax and non-tax) advising on restitution claims involving national or EU public bodies. Rafal Zakrzewski British Tax Review No. 3, 2012 Williams...presents a clear and well-argued case for a public law of unjust enrichment. Her approach is thoughtful and considered covering key cases in English, French and EU law, and focuses on an area of law of particular topicality...While her argument does, as she states, remain normative, lacking case law support, she nevertheless provides a lucid and well-researched argument for reform. Williams must thus be praised for drawing together and critically appraising the leading cases in this field and for providing valuable insight into this developing area of the law. Paula Giliker European Law Review Volume 36, 2011 Unjust Enrichment and Public Law is an important contribution to this topical subject. The discussion of English law is comprehensive and well argued, and will interest both public and private lawyers. Unjust Enrichment and Public Law is a well-written and well-presented book, which does much to advance our understanding of this difficult area of law. It deserves the attention of lawyers across the public/private divide. Paul S. Davies The Law Quarterly Review Volume 127, July 2011

• Part 1 Unjust Enrichment and Public Law in England and Wales 1-Definitions and Controversies 'RESTITUTION' OR 'UNJUST ENRICHMENT' Using the Map The Criteria for a Claim in 'Autonomous' Unjust Enrichment 'PUBLIC BODIES' AND 'PUBLIC LAW' CONCLUSION 2-Woolwich and the Creation of the Public Law Reason for Restitution THE FACTS THE BACKGROUND TO THE CLAIM A WHOLLY PRIVATE APPROACH? POTENTIAL UNJUST FACTORS AVAILABLE TO THE WOOLWICH Duress or Colore Officii Inequality No Consideration Failure of Consideration Mistake of Law TWO NEW OPTIONS FOR RECOVERY WHAT IS THE WOOLWICH UNJUST FACTOR? Illegality Incapacity Absence or failure of basis Inequality A WHOLLY PUBLIC APPROACH: COULD RESTITUTION SIMPLY BE A RESPONSE TO A PUBLIC LAW EVENT? THE SOLUTION: A HYBRID APPROACH 3-The Scope of the Public Law Reason for Restitution THE SCOPE OF THE PUBLIC LAW REASON FOR RESTITUTION: EIGHT KEY QUESTIONS Need There Have Been a Demand for the Public Law Reason for Restitution to Operate? Need There Have Been a Protest for the Public Law Reason for Restitution to Operate? To What Extent is the Public Law Reason for Restitution Overridden by Statute? What Exactly Does the Claimant Recover? Is it Always Necessary to Bring Two Separate Cases, One Action for Judicial Review and One Private Law Claim? Over What Subject Matter does the Public Law Reason for Restitution Extend? What Sort of Invalidity Triggers this Reason for Restitution? Which Kinds of Body Will Give Rise to this Reason for Restitution? THE SCOPE OF THE PUBLIC LAW UNJUST FACTOR: RESTITUTION FOR PUBLIC BODIES The 'Swaps' Cases 4-A Hierarchy of Reasons for Restitution THE ADVANTAGES OF THE PUBLIC LAW REASON FOR RESTITUTION OVER THE PRIVATE LAW UNJUST FACTORS REASONS FOR RESTITUTION AND TIME LIMITS: IS A HIERARCHY POSSIBLE? Deutsche Morgan Grenfell v IRC FURTHER ARGUMENTS AGAINST THE HIERARCHY Does Mistake Provide a Broader Ground of Recovery than the Public Law Reason for Restitution? HOW WIDE ARE THE EFFECTS OF THE PUBLIC LAW REASON FOR RESTITUTION? How Wide is the Finding of Ultra Vires? How Far does a Claim in Unjust Enrichment Extend into Consequential Loss? EVIDENCE FOR THE HIERARCHY AND THE ISSUE OF 'CLOSED' SWAPS CONCLUSION 5-Defences WHAT GENERAL IMPLICATIONS DOES THE HYBRID NATURE OF THE REASON FOR RESTITUTION HAVE FOR DEFENCES? TIME LIMITS PRIVATE LAW DEFENCES Change of Position Estoppel Bona Fide Purchase Impossibility of Counter-Restitution Submission to an Honest Claim Ultra Vires Passing On SPECIAL DEFENCES IN PUBLIC LAW UNJUST FACTOR CASES Fiscal Disruption The Law Commission's 'Special' Defence of Exhaustion of the Statutory Mechanism Prospective Overruling CONCLUSIONS AND FURTHER IMPLICATIONS Part 1 Conclusions and further implications Part 2 Unjust Enrichment and Public Law in France 6-Public Body Unjust Enrichment Claims in France; Lessons for England and Wales THE PUBLIC/PRIVATE DIVIDE IN FRANCE THE FRENCH LAW OF UNJUST ENRICHMENT Enrichissement Sans Cause Repetition de l'indu Gestion d'affaires ENRICHMENT WITHOUT CAUSE AND PUBLIC BODIES Quasi-Contracts are Automatically Adjusted in their Application to Public Bodies If Courts Have to Choose Between Two Events, Both of which are Actually Relevant to the Basis of the Claim, Some Courts Will Choose One, and Others the Other As well as Adjusting its Quasi-Contracts to Take Account of Public Bodies, French Law Also Distinguishes between Public Law Rules and Public Law Procedure, so that even within the Private Procedure Adjustments can be Made to Take Account of the Public Nature of one of the Parties to the Claim The 'Absence of Cause' Approach does not Necessarily Provide a Better Solution for Public Body Enrichment Cases The Need to Accommodate Public Bodies in Private Claims has a Tendency to Change the Rules of Private Law Itself CONCLUSION Part 3 Unjust Enrichment and Public Law in the European Union 7-Unjust Enrichment and the EU Institutions AN EU LAW OF UNJUST ENRICHMENT? UNJUST ENRICHMENT AS A GENERAL PRINCIPLE OF EU LAW Staff Cases Annulment Cases Three Party Cases UNJUST ENRICHMENT: ONLY A 'GENERAL PRINCIPLE' OF EU LAW CONCLUSION 8-Unjust Enrichment in National and European Law, and the 'Remedies' Jurisprudence of the ECJ HISTORICAL DEVELOPMENT OF THE RELEVANT EUROPEAN UNION LAW THE MEMBER STATE/EU DIVIDE: REMEDIES IN NATIONAL COURTS FOR BREACH OF EUROPEAN LAW The Principles of National Procedural Autonomy, Equivalence and Effectiveness, and the Three Phases of the ECJ's Case Law UNJUST ENRICHMENT AND ULTRA VIRES IN NATIONAL AND EU LAW; TWO DIFFERENT MODELS FOR ANALYSING THE DIVISION OF LABOUR BETWEEN THE MEMBER STATES AND THE EU Two important factors against Model 2 Cases in which a Member State or a National Intervention Agency Levies Money in Contravention of EU Law Cases in which an NIA or the EU Pays Out Money in Breach of EU Law which it then Seeks to Recover IS THERE AN EU LAW 'EVENT' OF ULTRA VIRES IN CASES INVOLVING BOTH EU AND NATIONAL LAW? CONCLUSION-THE IMPACT OF EU LAW ON NATIONAL UNJUST ENRICHMENT CLAIMS INVOLVING PUBLIC BODIES