The public law of restitution

Restitution is the body of law that responds to unjust enrichment. It is a private law doctrine but, like other fields of private law such as the law of torts, it intersects significantly with public law. This article examines the seminal case of Woolwich Equitable Building Society v Inland Revenue Commissioners, in which the House of Lords held that an unlawful demand for a payment of tax which was not due was an unjust factor capable of making out unjust enrichment and enabling the claimant to obtain restitution of the money paid and interest. This was a significant step forward for restitution generally but was of specific interest to public lawyers, since it links an ultra vires demand to a monetary remedy, something which is not available in judicial review. This article will look at the basis of the Woolwich factor and whether and how it might be accepted into Australian law.