A damning report by the chief inspector of borders and immigration has raised serious questions over the UK Border Agency's competence.

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The findings of an inspection into the UK Border Agency's handling of legacy asylum cases has uncovered a catalogue of failures in the beleaguered government department.

Thousands of immigrants have been allowed to stay in the UK without proper checks because of a huge backlog of cases, while almost 100,000 pieces of post were left unopened, the new report reveals.

Security checks were not carried out properly, with applications placed into an archive of unresolved cases after "minimal work", while the agency assured MPs that "exhaustive" checks had been carried out.

The report reveals how over 147,000 cases remain unresolved after the agency claimed in the summer of 2011 that they had been cleared. Asylum seekers who had no grounds to stay in the UK were granted the right to remain because they were left waiting so long for their cases to be resolved.

Those who waited longest got the worst deal, conclusion for them has been a grant of more temporary leave. Judith Dennis, Refugee Council

Labour shadow immigration minister Chris Bryant has described the chief inspector's report as "utterly damning" and called border staff's efforts "slapdash".

The Commons home affairs select committee has previously warned that the border agency was unable to fulfil basic functions and was tarnishing the reputation of the government.

The continued failures have angered groups on both sides of the immigration debate. The agency has been criticised for failing to control the nation's borders as well as leaving asylum seekers in uncertainty.

Judith Dennis, policy officer at the Refugee Council, has accused the border agency of causing "ongoing suffering" for people forced to wait years for a decision and highlighted the human cost of an inefficient system.

"They must urgently put resources in to ensuring people are finally given a right and fair decision," Judith Dennis explained.

"They are unable to get on with their lives, many living without support or access to basic services. We know from our own work that in many cases, people's mental and physical health deteriorates as a result."

"Those who waited longest got the worst deal - conclusion for them has been a grant of more temporary leave. It is only fair that those who are allowed to stay should be given permanent residence; after years of living in limbo."

'No excuse'

A sample of 135 UKBA files showed each case had lain dormant for an average of 87 months, the shortest period was six months, but the longest was over 17 years. Just 34 applicants had been recorded as absconders on the police national computer.

Sir Andrew Green, chairman of Migration Watch, a group campaigning for tougher border controls, has called the report "another chapter in a sorry tale" blaming a "shambolic legacy of outstanding asylum applications".

"They are seriously under resourced to cope with the expanding load of asylum and immigration cases. That is no excuse for the Home Office being less than frank about the situation but the fundamental problem is that they are reduced to sticking fingers in the dyke."

Among the numerous failings, Chief Inspector of Borders and Immigration John Vine found that an examination of controlled archive cases showed security checks had not been undertaken routinely or consistently since April 2011.

"No thorough comparison of data from controlled archive cases was undertaken with other government departments or financial institutions in order to trace applicants until April 2012," Mr Vine explained.

"This was unacceptable and at odds with the assurances given to the Home Affairs Select Committee that 124,000 cases were only archived after 'exhaustive checks' to trace the applicant had been made."

Limited resources were highlighted as a significant impediment to case clearance, with timescales given to applicants frequently missed, even where legal action was threatened.

A spokesman for the border agency claimed they were implementing "every recommendation from the report" and conceded that UKBA is a "troubled organisation with a poor record of delivery".

"The Border Force is now an independent organisation and its performance is improving. And UKBA has a transformation plan that will put the agency on a surer footing."