David Cameron, the Prime Minister, has been warned that measures designed to keep illegal immigrants out of Britain could collapse unless he pledges to address a new immigration crisis. As violent clashes took place in an illegal refugee camp in Calais, French officials wrote to Mr Cameron to say they would no longer support British border officials working in France. Philippe Mignonet, the deputy mayor and immigration chief at Calais, told The Telegraph he was losing patience with a treaty which allows British border guards to check passports in France before passengers board ferries or Channel Tunnel services. The British border was moved to France in 2003 as part of a deal to close the infamous Sangatte refugee camp, and to stop illegal immigrants reaching British soil to claim asylum. ‘We are suffering in Calais. Calais is a city, not a country. We are suffering by having the English border on its territory,’ said Mr Mignonet.