Immigration chiefs have denied a "stealth amnesty" of failed asylum seekers as it was revealed 19,000 had been allowed to stay in the UK.
They were part of a backlog of up to 450,000 failed asylum seeker cases discovered last year by officials.
The figures were in a leaked letter from immigration chief Lin Homer to home affairs committee chair Keith Vaz.
The Tories said it was a "stealth amnesty" but Ms Homer said each case was "judged according to the law".
Previous home secretary John Reid announced the scale of the backlog in asylum cases July last year, which he said was between 400,000 and 450,000.
He pointed out that the figure referred to case files, rather than individuals, and said they were "riddled with duplication and errors".
In her letter Ms Homer, the chief executive of the Border and Immigration Agency, said officials were on course to clear the backlog by 2011 and were speeding up the process.
Ms Homer said: "To date we have concluded around 52,000 cases, of which about 16,000 have led to removals, 19,000 have led to grants of leave and 17,000 have been closed due to previously erroneous or duplicate records...
"Now that the process has been put into operation, the number of cases being concluded is increasing."
"From July to November this year 29,000 cases were concluded and we will continue to escalate performance.
"We remain confident that we are on track to conclude the cases by September 2011."
Newspapers reported that if approvals continued at the current rate of 36.5% then 165,000 asylum seekers would be allowed to stay.
Mr Vaz told BBC Breakfast that figure seemed "far too high".
But he added: "It's right that we need to deal with the backlog, even on those figures, reading the newspapers, it's going to take until 2010 to clear that backlog."
He said he had not yet seen the letter from Lin Homer but was keen for her to appear before the home affairs committee to "see why on earth this is happening".
The Conservatives say it will take decades to deal with the backlog of asylum seekers.
Shadow home secretary David Davis said government "incompetence" meant there was effectively a "stealth amnesty".
Mr Davis said: "After 18 months' effort and on their own numbers the government can still only claim to have removed 3% of the backlog.
"At this rate it will take decades to remove the backlog, by which time we will have another backlog since the government is also failing to meet its target of removing more failed asylum seekers than arrive.
"Since these are people who had not been granted the right to remain in the UK, this combination of low removal rates and lengthy delays means this is effectively a stealth amnesty.
"This is a policy by incompetence rather than decision."
Lib Dem home affairs spokesman Jeremy Browne said the revelations showed the asylum system was "failing in every direction".
"It's time for a fully independent asylum agency, as in Canada, to restore basic competence and humanitarianism to our asylum process," added Mr Browne.
In response to the amnesty allegation, Ms Homer said: "This is not an amnesty. Individuals are judged according to the law. If someone has no right to remain in the UK, they will be removed - forcibly if necessary.
"Last year we removed record numbers of people. To date we have concluded 52,000 cases. Two thirds have either been removed, or discovered to be duplicate files or errors."
In the letter to Mr Vaz, Ms Homer said she expected the government would meet its target of deporting 4,000 foreign national prisoners in this calendar year.
She also revealed that in four cases, foreign prisoners had not been considered for deportation before they were released at the end of their sentence.
Two individuals had been detained, and two others had not yet been traced.
The cases involved only short sentences.