However, there is legislation to cover such incidents, referred to as 'dishonestly retaining wrongful credit', and as mentioned previously, can result in up to a 10 year prison sentence. Section 24A of the 1968 Theft Act makes it clear that any money knowingly received in error must be repaid.

UK law

Source: https://www.wilson-nesbitt.com/news-updates/Criminal/7463/Public-unclear-on-law-on-retaining-wrongful-credit