Immigration inspectors have discovered more UK Border Agency (UKBA) backlogs, totalling more than 16,000 cases.
The chief inspector of immigration said the latest backlogs, relating to requests to settle through marriage, were "unacceptable".
The backlogs included people waiting a decade to hear if their partner had permission to live in the UK.
Immigration Minister Mark Harper denied the Border Agency was a "shambles", and said managers were "getting a grip".
The marriage or civil partnership-related backlog is thought to be the 10th category of unresolved cases that has emerged in the past two years.
Inspectors looked at how well the agency was handling applications from people from outside the European Economic Area who have a partner already in the country, such as a husband or wife who is British.
John Vine, the independent chief inspector of borders and immigration, said the majority of decisions were reasonable and caseworkers checked whether applicants were known criminals.
But he said his team had found a backlog of 14,000 cases where the UKBA failed to deal with requests to reconsider decisions after an initial rejection.
When inspectors visited a UKBA office in Sheffield they found a further backlog of 2,100 "complex" temporary migration cases. These included 180 marriage entry or settlement applications which had not received an initial decision. Some dated back to 2003.
One inspector said the unresolved applications had been effectively "dumped" on the Sheffield team after being transferred in a box from the UKBA's Croydon offices. Officials have since dealt with these cases.
At the time of the inspection last year, the marriage-related backlog was growing at a rate of 700 cases a month. Caseworkers told inspectors they could not deal with them until they had received new policy guidance.
However, a senior manager told inspectors that agency chiefs were unaware that these cases were not being dealt with and staff could make decisions without waiting for new policy.
Mr Vine said: "I don't think I should be discovering these backlogs. The agency should know about its workload. It should prioritise its resources and, at the very least, have a plan to deal with some of the things that we come across in inspection.
"For people to be in such a backlog of cases is not acceptable and I urge the agency to deal with the cases swiftly. To wait such a long time, even if your case is complex, is completely outside any service standards."
The immigration minister said: "We inherited an agency which had a lot of problems, we've got a new management team to deal with it. They're getting a grip and dealing with it."
Mr Harper said 14,000 of the cases "weren't people waiting for a decision", but people "who didn't like the decision and didn't go through the proper appeal mechanism".
"And what the Border Agency should have said in the past, it should have said 'no, there's an appeal process, if you don't like the decision, appeal'," he told BBC Radio 4's Today Programme.
"But it didn't do that, it kind of accepted these requests [and] didn't have a process to deal with them.
"We have now got a clear policy, published, about how we deal with those - which is people should appeal properly and those people who have been refused are not allowed to stay here. Should leave the country and we will be taking steps to make sure that they do."
Lin Homer, who headed the Border and Immigration Agency and later the UK Border Agency, between 2005 and 2010, is currently chief executive of HM Revenue and Customs.