At least 150,000 migrants have been refused permission to stay in the UK but the authorities do not know how many have left, a watchdog has warned.
John Vine, chief inspector of the UK Border Agency (UKBA), said there is no clear strategy to find out what proportion of this growing number of migrants is still in the UK illegally.
Tracking these absconders down and removing them from the country is not seen as a priority for the agency, Mr Vine said.
He added: “There are over 150,000 cases nationally of migrants who have been refused an extension of stay in the UK. The agency does not know how many of these individuals have left the country or who are waiting to be removed.”
He added: “I believe it can and must do more to demonstrate it is dealing with this issue in a more proactive manner.
Shadow Home Secretary Yvette Cooper described Mr Vine’s report as “damning” for the Government. Keith Vaz, chairman of the Commons Home Affairs Select Committee, said: “I am astonished that the UKBA has no idea where 159,000 individuals, the size of a city like Oxford, have gone since their application was rejected.”
Immigration Minister Damian Green said: “Under the last government there was no effective strategy in place to ensure migrants left at the end of their time in the UK.
“The UK Border Agency is now working through a group of potential overstayers to identify those who have not left.”
Earlier this year Theresa May, the Home Secretary, announced that the UK Border Agency would be split in two after a damning report into the relaxation of airport checks.