British and Irish nationals do not need to use the share code system. Instead, they can prove their right to work by showing their British or Irish passport. Alternatively, they can provide a UK birth or adoption certificate, an Irish birth or adoption certificate, or a certificate of registration or naturalisation as a British citizen. They must also provide an official letter or document from a previous employer or a government agency such as HM Revenue and Customs (HMRC), the Department for Work and Pensions (DWP) or the Social Security Agency in Northern Ireland. The letter must show the person’s name and National Insurance number.