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 have warned.
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, said the Commons Home Affairs Select Committee.
"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," said the third damning report of the year into the UKBA's work.
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, said the committee.
Immigration minister Damian Green said the UKBA had improved from a state of "complete chaos" when the Government took office two years ago.
Speaking to the BBC Radio 4 Today programme, Mr Green said: "It is getting better slowly, probably too slowly than most people would want - some areas are getting better faster than other areas. The asylum service is immeasurably much better than it was three or four years ago."
Mr Green said the Government had to "clean up" a legacy of mistakes on dealing with foreign criminals and ensure the errors were not repeated. He added: "We're not stopping here and I'm not saying the system is perfect yet."