The backlog of immigration cases at Britain's troubled border service has hit a "staggering" half a million people and at the current rate of progress will take nearly four decades to clear, a group of MPs has warned.
A rise in the number of foreign-national offenders living in the community as they await deportation was also discovered by the Home Affairs Select Committee in its latest report into the work of the now-defunct UK Border Agency (UKBA).
Migrant Watch warned that the system was in "in chaos" and said it hoped the figures were a "wake-up" call.
The committee warned that a recent move to scrap the agency and replace it with two new divisions - one in charge of immigration and visas, the other with border enforcement - was in danger of being an "exercise in rebranding".
It discovered that in the final quarter of last year, spending on external consultants at the agency rocketed from £27,000 in the previous three months to more than £500,000.
"The backlog of cases has now hit a staggering half a million people. This could fill Wembley Stadium to capacity six times over," committee chairman Keith Vaz MP said. "At the current rate it will take 37 years to clear and the Home Office cannot confirm that this is the last of the backlogs."
He added: "Theresa May described the UK Border Agency as 'closed, secretive and defensive', however, despite abolition nothing appears to have changed apart from the name. If people at the top are not replaced this will only be an exercise in rebranding as has happened in previous reincarnations.
"There should be no more bonuses paid to any senior management at the Home Office until the backlogs are cleared."
Immigration Minister Mark Harper said: "The UK Border Agency was a troubled organisation for many years, which is why the Home Secretary took the decision to split the agency in March this year.
"The new UK Visas and Immigration Service has a clear focus to improve visa performance and customer service, while the Immigration Enforcement Command concentrates on those who break our immigration laws.
"Both now report directly to ministers, delivering greater transparency and accountability.
"It will take a long time to clear the backlogs we inherited - but through the changes we have made we are in a much stronger position to do so."
After a raft of damning reports, Home Secretary Theresa May abolished the UKBA and replaced it with UK Visas and Immigration and an Immigration Enforcement command, which were brought back under the control of ministers.
The new head of the UK Visas and Immigration section recently told the committee that Britain's immigration service will never be completely fixed.
Director general Sarah Rapson warned that the service will never be seen as ''perfect''.
In its report, the committee said: "We are concerned this is an admission that Ms Rapson does not have the resources necessary to 'fix' the service."
The total number of cases in the migration backlog has reached 502,462, the committee said, compared with 321,726 in its previous report.
A total of 4,102 foreign-national offenders were living in the community awaiting deportation in the final three months of 2012, an increase of 122 on the previous three months. Some 65% of these cases are more than two years old.
The committee discovered that the length of time taken to deport an a foreign-national offender has increased by nine days in the same period to 127 days.
The MPs expressed concern that the former chief executive of the UKBA, Rob Whiteman, had not been "as open with the committee as he should have been" when discussing the number of cases in progress within permanent migration applications.
Whiteman, who will leave the Home Office next month to become chief executive of the Chartered Institute of Public Finance and Accountancy, did not see his salary reduce from £175,000 a year, despite seeing his department split into four separate units, effectively reducing its size by 75%.
The committee added that it was "deeply concerned" to discover that spending on external consultants in the final three months of last year increased 20-fold from £27,000 in the previous quarter to more £500,000.
The group of MPs said: "The use of external consultants has been actively discouraged across Whitehall as spending cuts take their toll on budgets. We expect the Home Office to clarify why this huge increase has occurred."
Sir Andrew Green, chairman of campaigner group Migration Watch UK, said: "The Government inherited a system in chaos.
"There have been signs of improvement but this new backlog of half a million cases is surely a wake-up call.
"The immigration system is struggling again and must be allocated substantially greater resources commensurate to the scale of the task and the importance the public attach to bringing immigration under control. The policy is now right but it cannot be implemented on peanuts."Suggest a correction