An "unacceptable" backlog of more than 16,000 immigrants waiting to hear whether they can stay in Britain was discovered in a fresh investigation into UK border controls, inspectors have said.
Some 14,000 applicants, growing at a rate of 700 a month, have already been refused the right to stay but are pleading with the UK Border Agency (UKBA) to reconsider.
And an additional 2,100 cases - shipped in a box from an office in Croydon to Sheffield - were still waiting for an initial decision at the time of the inspection, with some dating back a decade. The UKBA said these have since been cleared.
The backlogs were discovered by the Independent Chief Inspector for Borders and Immigration John Vine as part of an inquiry into applications to remain in Britain on the basis of marriage. Mr Vine said: "This is completely unacceptable and I expect the Agency to deal with both types of case as a matter of urgency."
The inspector said he was "surprised" to discover the UKBA is also failing to check whether applicants earn enough to look after themselves without having to rely on state handouts.
Meanwhile, a separate inspection into how the UKBA and Border Force deal with criminals at ports, such as Heathrow Airport, discovered that the policy of swift removal is being rendered ineffective by the level of immigrants claiming asylum.
UKBA staff told the inspector that the agency was sitting on 14,000 refused cases that the UKBA was asked to reconsider because there was "no policy" on how to deal with them. But further investigation discovered "confusion" among staff, with one senior manager informing the inspector there was nothing to stop the cases from progressing.
Sir Andrew Green, chairman of campaigners Migration Watch UK, said: "This is yet further evidence of the chaos in the immigration system from which they are taking years to recover."
A Home Office spokeswoman said: "The agency is taking action to deal with historic backlogs and has a transformation plan that will put the agency on a surer footing. This group of people have already been refused but are trying to circumvent the appeals process by requesting an informal 'reconsideration'.
"We've changed the rules to make clear that those not happy with the original decision should re-apply or appeal and if they choose not to, they should leave the UK voluntarily. We are contacting them to make sure they do this, but if they refuse we will enforce their removal."