Almost 4,000 foreign criminals whom the Government wants to deport are at large in the community, figures showed today.
Some 2,500 were released from jail more than two years ago and more than 800 have been released for more than five years, UK Border Agency (UKBA) statistics showed.
Rob Whiteman, the agency's chief executive, admitted foreign criminals were not being deported quickly enough as he blamed the lengthy judicial processes, difficulties obtaining documents from other countries and deliberate attempts to frustrate the system for the delays.
One foreign criminal frustrated attempts to deport him nine times before he was sent back earlier this year, Mr Whiteman told MPs on the Commons Home Affairs Select Committee.
One trick used by offenders is to tell officials on arriving home that they are not from that country, he added.
"I agree with you that it's taking too long," he said.
"We do not want foreign national offenders to be in the community for several years before they are deported."
But he said that in 90% of cases, courts rather than the UKBA had ruled that the criminals should be released because there was no realistic prospect of a quick removal.
"Our view is that they should be held in detention," he said.
Mr Whiteman blamed several factors for the delays, including the length of time it can take for cases to go through the system, the multiple rights of appeal on different points of law, difficulties obtaining documents from foreign countries and problems with people trying to obstruct the system.
Some case law which puts the interests of children above the interests of deportation can also cause difficulties, he said.
Asked about the numbers, he added: "I don't think I can guarantee that it will come down rapidly."
Some 3,900 foreign national offenders who are subject to deportation action were living in the community as of April 4, the UKBA figures showed.
These include 817 offenders who were released more than five years ago, 1,650 who were released more than two years ago, and 664 who were released between one and two years ago, a breakdown given in a letter from Mr Whiteman to MPs on the committee said.
A further 31 were released between six months and a year ago and 327 were released within the previous six months. There were "data quality issues" with another 166 cases.
Earlier, Michael Ellis, the Tory MP for Northampton North, told Mr Whiteman: "Your own figures show there were 3,900 foreign national offenders subject to deportation action who are living in communities as of six weeks ago.
"Now I accept that 2,467 were released over two years ago and 817 were released over five years ago, but people are getting fed up with this.
"The fact of the matter is that despite the previous incompetences you've inherited as far as the legacy, which I appreciate is the case, there's too many people who are foreign nationals committing criminal offences who surely should have been deported and it's taking too long."