Over 280,000 failed asylum seekers could still be in Britain despite extra cash being spent to remove them.
Minister Tony McNulty says removals have been increased
In September 2004 Tony Blair said monthly removals should exceed rejected applications by the end of 2005.
But according to the National Audit Office (NAO), the immigration authorities are struggling to meet the prime minister's demands.
Immigration Minister Tony McNulty said the government had upped removals and cut asylum applications significantly.
PEOPLE REMOVED FROM THE UK
According to NAO, drop in removals 2004-05 mainly due to previously removable failed asylum applicants from EU accession countries having right to remain in UK following EU enlargement in May 2004
Excludes dependants of asylum applicants
"We remain committed to our aim of removing more people on a monthly basis by the end of 2005 than there are new unfounded claims," he added.
"In 1996 the number of removals was equivalent to only 20% of predicted unfounded claims, now that proportion is around 50%."
Problems found by the NAO included delays in obtaining travel documents, poor co-ordination between different branches of the system and insufficient use of an existing assisted voluntary return programme.
The NAO's report 'Returning Failed Asylum Applicants' notes that between 1994 and May 2004 363,000 asylum applications were rejected but just 79,500 people removed - leaving 283,500.
It notes that some of those still in the country would have been granted leave to remain or would now be able to stay thanks to EU expansion - and some might have left the UK voluntarily.
In May 2004 the database of the Immigration and Nationality Directorate (IND) identified 155,000 failed applicants as potentially removable, although that figure excludes cases which predate the database's introduction in 2000.
Neither figure incorporates people who overstayed their leave to remain in the UK, a number that has not been quantified.
The NAO report says that in the five year period from 2000/1 to 2004/5 the IND increased the number of failed applicants being returned to their country or origin or a safe third country by 35% up from 8,960 to 12,110.
But the removal or voluntary return of 1,000 a month in 2004/5 was significantly less than the number of unsuccessful applications, which averaged around 2,150 each month.
The NAO noted that the IND spent £300m in 2003 to 2004 on removals and voluntary returns; £308m on supporting failed applicants and legal costs associated with applicants appealing against being turned down were on top of that bill.
REMOVALS v UNSUCCESSFUL APPLICATIONS
Estimated number of newly refused applications based on number of cases with outright first refusal in the year, less cases where applicant successfully appealed
According to NAO, high number of newly refused applications recorded 2000-01 reflects actions taken by IND to address backlog of undecided applications and continued high rate of new asylum applications
Edward Leigh, the Conservative MP who chairs the Commons public accounts committee for which the NAO reports, said: "It is shocking that IND cannot give a solid estimate of how many failed applicants are still in the UK.
"But the NAO tells us it could have been as many as 283,000 in May 2004 - which means an even higher number today."
NAO chief Sir John Bourn said: "The Immigration and Nationality Directorate has made progress but needs to do a better job to track and manage cases and do more to encourage failed asylum applicants to return home voluntarily."
Sir Andrew Green, chairman of Migrationwatch UK, said: "The security implications of this are clearly serious. The chaotic state of our asylum and immigration system becomes daily more apparent."
Separately, ministers have announced that four areas of the UK will trial a new scheme to help those asylum seekers who have been accepted for settlement as refugees.
The Sunrise project aims to help refugees integrate into British society far more quickly by giving them expert guidance on rebuilding their lives in Britain. The trials will take place in Glasgow, Leeds, West London and Manchester.
TOP 1O REMOVED NATIONALITIES
Based on claimed nationality of person removed and includes removals to their country of origin or to a safe third country through which they were found to have come to the UK
Excludes dependants of asylum applicants