The political focus on asylum was one of the reasons why action to consider deporting foreign prisoners was not taken sooner, according to two former Home Office officials.

Sir John Gieve, former permanent secretary to the Home Office, gave evidence to the Commons home affairs committee alongside former Immigration and Nationality Directorate head Stephen Boys Smith.

Boys Smith said: "I think it's important, if I may, to remind the committee of the way in which asylum and all the problems associated with it were the dominant issue for IND as an organisation, and I have to say the dominant issue for ministers and perhaps for the wider public [was] discussion on immigration."

He said during his time in office the department had not ignored other priorities like removals.

He said: "We were trying to move forward in a constructive way but reflecting the proper ministerial priority on asylum."

Sir John said last autumn when he appeared before the Commons public accounts committee - which bought the subject of foreign criminals being released without deportation to light - the focus of the session was on dealing with the backlog of asylum cases.

He said: "I think it was inevitable we would give top priority to that.

"Everyone knew that meant other bits of the organisation were stretched and weren't getting the attention they wanted, progressively over the years we started to try and get through that, particularly in 2004, but this was a crying political and organisational demand to nail this down."

Asked if it was a conscious decision to ignore the subject of deporting criminals in favour of asylum, Sir John said there was "no explicit trade off".

Asked when the extent of the problem came to light, Boys Smith said: "People simply weren't aware of the totality of the problem.

"They were aware that there were people coming out of prison but nobody had measured the problem in the round."

Sir John said he did not know when ministers first became aware of the problem. "I don't know when they knew, it depends when they asked," he said.

"My attitude to this was that I knew that we were expanding the resources going into the unit to deal with foreign prisoners, I knew and I think ministers knew that there was a problem of a backlog there, that we needed to put more resources in and they were keen that we should do so.

"At the time it seemed to me a statement about what had happened over a period of years because of the under-resourcing of a unit we were addressing with the minister's knowledge."