Unjust enrichment can affect all citizens. It covers situations, for example, where payments are made by mistake which could include anything from a phone bill which has been paid twice to a mistakenly paid tax bill worth millions.
Research into this area of the law by Professor Birks and Professor Burrows has stated that all claims based on unjust enrichment involve four questions: (1) ‘The enrichment question’: has the defendant been enriched? (2) ‘The at the expense of question’: was the enrichment at the claimant’s expense? (3) ‘The unjust question’: was the enrichment at the claimant’s expense unjust? (4) ‘The defences question’: does the defendant have a defence? If the answer to the first three of these questions is ‘yes’ and the answer to the fourth question is ‘no’ then the claimant has a right to restitution. This four part framework has become accepted as the best way for judges to decide cases on the English law of unjust enrichment. The work of Birks and Burrows has been mentioned in many judgments in England and Wales and other jurisdictions including Australia, Canada and Hong Kong.