Two prisons in England are holding only foreign nationals to speed up their deportation, a minister admitted today.
The justice minister David Hanson said the policy was an attempt to speed up deportation in a "cost-effective and efficient" way.
The two all-male jails are Bullwood Hall in Hockley, Essex, which holds 154 prisoners, and Canterbury prison, which holds 284 men serving less than four years.
"What we're trying to do is to have an experiment to see whether we can speed up the deportation of foreign national prisoners, particularly those coming towards the end of their sentence," Mr Hanson told BBC Breakfast.
"And the two prisons particularly have immigration officials working with them very closely, five in each prison, to help speed up the deportation of prisoners when they come to the end of their sentence.
"We've actually increased the level of deportation quite significantly over the past two years. Two years ago 1,500 prisoners were deported, last year 2,500, this year, in line with the prime minister's commitment, we're on target to achieve 4,000."
Mr Hanson said there were agreements in place with more than 100 countries for prisoners to serve their sentences in their home countries.
"But we can't just deport individuals on receiving their sentence in all cases, because there are a range of issues relating to that," he said.
Mr Hanson said the two prisons had been focusing exclusively on foreign nationals for about 18 months and the experiment was "working well". He said there were around 11,000 foreign criminals across the prison system.
The justice minister rejected the idea that foreign prisoners could be given short sentences so they could be removed from Britain more quickly.
"Foreign national prisoners are no different than any other prisoner," said Mr Hanson. "If they've committed a crime in England and Wales they will be sentenced to the sentence they would get, whether they were British, or Czech or Polish or any other nationality."
He told BBC's Radio 4's Today programme that he did not know whether the trial would be extended "because we are evaluating it".
And he said there had been "no attempt to keep the matter secret".
"When parliament asked questions, we talked about foreign prisoners. The local press in Kent and Essex has been briefed on this topic."
The shadow justice secretary, Nick Herbert, said he did not object to foreign prisoners being kept in different jails.
"The problem is why haven't more of them been deported, at a time when the prisons are chock-a-block full," he told GMTV.
Frances Crook, of the Howard League for Penal Reform, told the programme that many of those being held were EU nationals who could return to the UK if they were deported.