'Illegal migrants' ordered to leave Britain had returned home years ago He added: "I've got 31 illegal migrants that aren't in the UK but are overseas. Who's to say exactly how many people are here illegally when they're not? Capita is contacting people on the list of possible illegal immigrants via email, phone or a text that states: "Message from the UK Border Agency. You are required to leave the UK as you no longer have the right to remain. However, among those it has incorrectly approached are a woman with a UK passport and a man with a valid visa who had invested £1 million in a British business. Critics have accused the Government of failing to get a grip on Britain's mounting backlog of immigration cases, with MPs warning in November that the system was "spiralling out of control." A Capita spokesman said: "Part of Capita's role is to identify those whose records suggest they are over-stayers but who have already left the UK. If we receive evidence to indicate that an individual has valid leave or has left the UK then records will be updated accordingly. The Home Office added: "Where our records show that people are here illegally, it is vital we are able to contact them as we are determined that they should return home."