The government is in talks to buy two prison ships to ease the current wave of overcrowding.
Police cells are already being used
An RAF camp is also being considered as one of a number of options to temporarily ease the pressure.
The Home Office has already sent out advice to courts to only jail dangerous and persistent offenders to help ease the situation in England and Wales.
One judge has already told a man who downloaded child pornography that the directive helped him avoid jail.
Prison numbers are currently hovering near the 80,000 mark with just 2,000 new places due by the end of the year.
The Home Office has considered a number of Army sites, as well as the RAF base now being looked at in the north of England.
Home Secretary John Reid has also explained why he rejected plans to place up to 400 prisoners at a military base in Dover late last year.
The base was just yards from a school where children of servicemen and women currently in Afghanistan were being taught.
The current overcrowding crisis has seen hundreds of prisoners housed in police cells and has prompted fierce criticism from the opposition.
The government will have 350 extra places in a prison on Merseyside in the spring, and says it will have 2,000 more by the end of 2007, but another 8,000 promised new places will not be ready for four years, with funding and sites yet to be fully approved.
In Wales, a man who downloaded dozens of indecent images of children received only a suspended prison sentence after a judge told him: "As of yesterday, I have to bear in mind a communication from the Home Secretary."
Judge John Rogers QC, the senior judge on the North Wales circuit, told Derek Williams, 46, of Penygwdwn in Blaenau Ffestiniog, he had to bear in mind "the current sentencing climate" in addition to the mitigation in the case.
Williams received a six-month prison sentence, suspended for two years.