The under-fire UK Border Agency must rid itself of its "bunker mentality" or risk raising suspicions that it is trying to mislead Parliament and the public, MPs warned on Wednesday.
Unclear data, which even the agency's own chief executive Rob Whiteman had difficulty in following, can be, at best, confusing and, at worst, misleading, the Commons Home Affairs Select Committee said.
"It is difficult to see how senior management and ministers can be confident that they know what is going on if the 'agency' cannot be precise in the information it provides to this committee," the third damning report of the year into the UKBA's work said.
It added that the agency was still failing to fulfil its basic tasks and risked damaging public trust in the government.
"The 'agency' must rid itself of its bunker mentality and focus on ensuring that Parliament and the public understands its work," the MPs said.
"Confusion over figures only risks suspicion that the 'agency' is attempting to mislead Parliament and the public over its performance and effectiveness.
"The only way the Home Office can allay and remove these fears is to clean up and clarify all the figures that are used in these reports."
Dame Helen Ghosh, the Permanent Secretary to the Home Office, should also set out how she "intends to clean up the use of statistics within the department", the committee said, adding the 'agency' was in fact "an integral part of the Home Office".
The wide-ranging report showed a fifth of foreign prisoners, some 1,060 criminals, who finished their jail terms in 2010/11 had still not been deported by November last year.
But the agency was unclear over which obstacles were blocking deportation and over which rights more than 520 other foreign criminals who had been allowed to remain in the UK had, the committee said.
It also found that six years after 1,013 foreign nationals were released from prison without being considered for deportation, only 397 have been removed or deported.
"Six years is far too long for this situation to be resolved and these cases should have been concluded long ago," the committee said.
It called for the authorities to ensure foreign defendants have the necessary travel documentation as soon as they are sentenced in a bid to see them deported once they have served their jail term.
Almost 20,000 asylum cases also remain unresolved and some 120,000 immigration cases are being written off because the applicant can no longer be found, it added.
Keith Vaz, the committee's chairman, said: "The reputation of the Home Office, and by extension, the UK Government, is being tarnished by the inability of the UK Border Agency (UKBA) to fulfil its basic functions.
"The foreign national prisoner issue and the asylum backlog were scandals which first broke in 2006, six years ago.
"UKBA appears unable to focus on its key task of tracking and removing illegal immigrants, overstayers or bogus students from the country."
He went on: "The so-called 'controlled archive', the dumping ground for cases where the UK Border Agency has lost track of the applicant, will take a further four years to clear at the current rate of resolution.
"This is unacceptable."
The committee also questioned why some 700,000 migrants were applying for multiple visas each year.
Its figures were based on records showing 120,841 of the 443,841 visa applications in August and September last year were from applicants who had already applied previously.
The MPs questioned "whether an applicant could have legitimate reasons for applying for three or more visas" and called for the agency to assess "the implications of imposing a limit on the number of times an individual can apply for a visa".
They also criticised the agency's refusal to recognise the term "bogus colleges" and the fact it gives advance warning of half of its college inspections.
All inspections of colleges sponsoring foreign students under tier four of the visa system should be unannounced in future, the committee said.
And it added that the mothballing of £9.1m Iris scanners at airports just five years after they were introduced "should not be repeated".
Any data collected on e-Gates trials should be published "to ensure it does not suffer the same costly investment in equipment which will not last", the report said.
Immigration Minister Damian Green said: "At the same time as clearing up the mistakes of the past, we are taking the action necessary to ensure the same errors will not be allowed to happen in the future.
"We are starting the deportation process earlier and removing foreign criminals more quickly than ever.
"We are now making better asylum decisions, ensuring cases are properly tracked, improving intelligence and speeding up removals.
"This government has chosen to publish more information than ever before, information which members of the public and parliament can use to analyse our performance and hold us to account."
Huffington Post blogger and US citizen Andrew Law said the UKBA was "Kafka-esque" and a "national disgrace, detailing despite how after living in Britain for eight years, being married to a British citizen and having degrees from British universities he had to challenge his deportation.
Now, the UKBA have taken his passport and he cannot go back to America without forfeiting his appeal.
"Despite the Immigration Tribunal allowing my appeal on 29 November 2011 to stay in the country with my English wife, the UKBA still hasn’t deemed it important to deliver my passport and visa back to me as of 5 April 2012, effectively denying me the justice the Tribunal Service sought to provide over twenty weeks ago. Surprisingly, legally there is no time limit for them to adhere to.
"What was a minor annoyance and long-running joke between my group of friends became something significantly more serious when I was told over the weekend that my father’s cancer had spread rapidly. It is vital I can go home," he wrote