Fewer than one in 10 asylum seekers in the backlog of more than 400,000 claims has been removed from the UK as 74,500 cases are written off as untraceable, MPs have been told.
Jonathan Sedgwick, the acting chief executive of the UK Border Agency, said just 9% of the cases led to removals while 40% - two in five of the asylum seekers - were granted indefinite leave to remain in the UK.
A further 74,500 cases have gone missing and will be consigned to a growing pile of applications unlikely to ever be resolved as no trace of the applicant can be found, figures showed.
"It's absolutely not the case that we've simply put these cases in a room and simply closed the door and forgotten about them," Mr Sedgwick said. "Each of those cases has been subject to the most exhaustive checks and scrutiny."
Giving evidence to the Commons Home Affairs Select Committee, he went on: "There is no trace of them. One conclusion from that may be that they've left the country, perhaps some of them have died. But we have done the most exhaustive things we reasonably and responsibly can."
Referring to the 161,000 asylum seekers who have been granted leave to remain, he conceded that some of these claims may have originally been refused, but the length of time taken to remove the individuals meant they had now gained new rights.
Mr Sedgwick denied it amounted to an "amnesty" that encouraged people to stay on after being refused asylum in the hope of being allowed to remain in the UK at some point in the future.
Labour MP Keith Vaz, the committee chairman, said: "We are concerned about the fact that only 9% of people have been removed, that you'll have granted indefinite leave to 161,000 people, 129,000 were errors and I think 19% are described as others and there are still 74,500 people in the controlled archive.
"Although of course there has been improvements, we're concerned where that bulk has disappeared to.
"One wonders with the cost at the UK Border Agency at the end of the day you've actually only removed 9%, was it all worth it? It's a very small proportion, that's what concerns the committee."