Media playback is unsupported on your device Media caption Keith Vaz: "Backlog equivalent to six times the capacity of Wembley stadium"

The backlog of unresolved immigration cases has grown to more than 500,000, a group of influential MPs has said.

The Home Affairs Committee said that at present rates it could take 37 years to clear.

In its latest report into the system, the cross-party committee questioned whether splitting up the UK Border Agency would change anything.

Immigration minister Mark Harper said the Home Office was now in a better position to clear backlogs.

In its last report, the committee said there were 11 separate backlogs totalling 320,000 open or unresolved cases in the immigration system.

Now it says there is a 12th backlog of 190,000 files called the "Temporary and Permanent Migration Pool".

'Rebranding exercise'

This brings the total to more than 500,000, which committee chairman Keith Vaz MP said was "staggering".

However, it is understood the Home Office disagrees with the figure because it is not new and has been over-counted by 40,000.

The committee said the backlog had emerged during its first evidence session with Sarah Rapson, the head of the new service dealing with visa and immigration applications.

IMMIGRATION BACKLOGS Q2 2012: 325,156

Q3 2012: 321,726

Q4 2012: 502,467

Source: Home Affairs Committee

Home Secretary Theresa May scrapped the UK Border Agency in March and said that two divisions, the first headed by Ms Rapson and the other for enforcements, would answer directly to ministers.

But the committee warned the change might be no more than a "rebranding exercise".

Mr Vaz told the BBC a "fundamental change" was needed in how officials tackled the backlog to resolve the issue "once and for all".

He said: "This is totally unacceptable. I know that the home secretary has abolished the UKBA, but we need to make sure that it's not just a rebranding exercise.

"We need new people at the top. We need a change of culture, but more than anything else we need to give them the resources that they need to clear the backlog."

'Overwhelmed'

He said no more bonuses should be paid to senior management at the Home Office until the backlogs were cleared.

Brodie Clark, the former head of the UK Border Force who was forced out of his job after being accused of relaxing passport checks, told BBC News that officials were being "overwhelmed by the sheer volume" of cases coming through.

He said splitting UKBA was costly and could actually hamper progress by creating "more of the working silos that have been an enduring criticism of the organisation".

NEW IMMIGRATION DEPARTMENTS UK Visas and Immigration Service

Immigration Enforcement Directorate

UK Border Force

Operational Systems Transformation The UKBA's astonishingly troubled history

Mr 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 Visa 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.

"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."

Rob Whiteman, who headed the now scrapped agency, is leaving the Home Office for another job. The Home Office said he was leaving voluntarily and there was no severance package.

Separately, the committee said it wanted to know why the former agency had spent more than £500,000 on outside consultants in the final quarter of 2012.