Many are because they have been in the country for so long hat the Home Office would have difficulty trying to remove them on human rights grounds because they have effectively settled here. 

Officials working through the so-called legacy backlog have so far examined 197,500 cases and there has been a 32 per cent approval rate, Lin Homer, the chief executive of the UK Border Agency, told MPs yesterday.

If that continues then some 144,000 will be able to stay once all the cases files have been looked at, in what the Tories have labelled an amnesty by the back door.

Damian Green, the shadow immigration minister, said: "Any progress is painfully slow on this."

The 450,000 files in the Case Resolution Programme were unearthed in 2006 after the foreign prisoners scandal.

Among them are claimants who should have been deported as far back as the mid-1990s.

Ministers have promised to work through all the cases by 2011, while also having to deal with all fresh asylum claims and those failed cases still awaiting deportation.

Miss Homer told the Commons Home Affairs Select Committee that she is confident that target will still be met.

Human rights laws will be the reason most cases were approved, either because it is unsafe to return the asylum seekers or because they have been here so long they now have families and are protected under the right to family life.

The list includes 5,150 from Zimbabwe, 4,900 from Pakistan and 4,500 from Somalia.

Miss Homer revealed that at least 7,000 so far may never be traced and their files have been archived. The Telegraph (UK)