A backlog of more than 150,000 migrants refused leave to remain in Britain could be living in the country illegally with their location unknown to border authorities, a watchdog has warned.
UK Border Agency (UKBA) officials did not know how many migrants they were supposed to track down, while as many as one in 10 overstaying visitors had not been told their time was up, John Vine, the independent chief inspector of borders and immigration, said.
"We did find that there are over 150,000 cases nationally of migrants who have been refused an extension to stay in the UK," said Mr Vine.
He said: "The agency does not know how many of these individuals have left the country or who are waiting to be removed.
"I also saw no evidence that there is a clear plan in place for the agency to deal with this stream of work to ensure this does not become another backlog."
Inspectors probed the performance of immigration officers in Hampshire and on the Isle of Wight and disclosed the size of the "migration refusal pool" – a list of workers refused permission to stay after their visas had expired.
Inspectors found that in Hampshire staff gave "contradictory" information and were unsure how many overstayers were still in the country.
Officials were supposed to be looking for three times as many illegal migrants as they actually were, the inspectors found.
About 40 per cent of migrant overstayers had not been served with forms telling them to leave the country.
Overall, there were 153,821 people in the refusal pool in October last year. That figure rose to 159,313 by December.
The shadow Home Secretary, Yvette Cooper, said the inspector's "damning conclusion" showed the Government was giving the issues very low priority.
"Out of 150,000 people refused leave to remain the Government seems not to know or care how many are still here," she said.
But Damian Green, the Immigration Minister, said UKBA was working through the backlog of overstayers.
"This summer, the UKBA launched a UK-wide operation to remove overstayers and we have already seen 1,800 removals since the campaign started.
"We are also working closely with other government departments to create a hostile environment which makes it much harder for migrants to live in the UK illegally."
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies