Courtesy of wikipedia:
Legal tender in England and Wales:
Bank of England notes are the only banknotes that are legal tender in England and Wales. United Kingdom coinage is legal tender, but in limited amounts for coins below �1.
Scottish and Northern Ireland banknotes, and Jersey, Guernsey, Manx and Gibraltar coinage and banknotes are not legal tender in England and Wales. However, they are not illegal under English law and creditors and traders may accept them if they so choose