The troubled UK Border Agency faces a backlog of cases equivalent to the population of Newcastle, MPs have warned.
Missing foreign criminals, failed asylum seekers, illegal immigrants and others refusing to leave the country make up more than 275,000 cases which the agency still needs to deal with, the Commons Home Affairs Select Committee said.
Keith Vaz, the committee's chairman, said the backlog, which will take years to clear, was unacceptable, adding that the agency seems to have "acquired its own Bermuda triangle".
"It's easy to get in, but near impossible to keep track of anyone, let alone get them out," the Labour MP said. "This is the first time that the committee has collated all the cases at the UK Border Agency that await resolution. This backlog is now equivalent to the entire population of Newcastle upon Tyne."
The latest damning report on the agency's work also said the committee did not believe the Government's aim of cutting the 260,000 student visas issued each year by a quarter would benefit the UK. Students should be excluded from the net migration figures instead, it said.
Britain would then continue to attract international students, a market worth £7.9 billion, and still be able to aim to meet Prime Minister David Cameron's pledge to cut net migration from 250,000 to the tens of thousands by 2015, the report said.
University chancellors and campaigners have urged Mr Cameron to class international students as temporary rather than permanent migrants, removing them from the figures. But Immigration Minister Damian Green has said students staying for more than a year are not visitors and their numbers affect communities, public services and infrastructure.
The report, looking at the agency's work between December last year and March, also called for the agency to make all its inspections of colleges unannounced, rather than giving them advance notice so key people and documents can be ready.
A Home Office spokesman said: "This report highlights the improvements we have made to tackle the huge backlog of cases we inherited. Over 2,000 overstayers have recently been removed following targeted enforcement activity, foreign national offenders are being removed more quickly and we are performing well against visa processing targets.
"Talented students are welcome in the UK, but we have introduced new powers to toughen up the system, keeping out the fraudulent and unqualified while ensuring genuine students continue to benefit from our excellent educational facilities. The report has raised some legitimate concerns about issues that we are aware of and are already tackling."