Immigration officials are working hard to reduce the length of time foreign prisoners spend in Campsfield House and other removal centres, the Government has insisted.

The Home Office, in an attempt to allay security fears following last weekend's breakout, released documents from the Border and Immigration Agency, which set out plans to begin preparations for the deportations of foreign prisoners at an earlier stage following sentencing - and well before their release from prison.

Lin Homer, chief executive of the BIA, said: "We are committed to increasing the pace and volume of removals and are on target to achieve 4,000 deportations of foreign prisoners this year.

"We now consider deportation eight months before the end of sentence and in many cases people can avoid lengthy detention by co-operating with the removal process."

In a letter written to the Home Affairs Committee in June 2006, passed to the Oxford Mail, Ms Homer said: "The rate of progress is inhibited by some internal processes, for example the training of the additional staff in deportation work, but also by some external and practical considerations."