An immigration minister has said it could take 10 years to deport all the illegal immigrants living in the UK.
There are no official estimates of illegal immigrants in the UK
Tony McNulty, speaking on BBC Two's Newsnight, said 310,000 to 570,000 was "roughly in the ball park" of how many illegal immigrants were in the country.
He said it would take a decade to remove them, on the basis that only so many could be deported each year.
Earlier Tony Blair had come under fire after saying there were no official figure estimates of illegal immigrants.
Mr McNulty said:"Assuming that we can find them, and assuming that people aren't going away of their own accord, it would take some time."
He said it would take "Ten years, if you are saying 25,000 per year."
"Remember too the illegal population as it is is multi-layered and segmented it's not just.. those climbing over fences," he added.
His comments follow a debate over illegal immigrants, after Mr Blair admitted there were no official estimates.
The row was originally sparked by the news that 1,023 foreign prisoners were released without being considered for deportation.
On Wednesday Mr Blair said he believed the vast bulk of foreign prisoners should be deported whatever the dangers in their home nations.
Downing Street later said some prisoners could avoid deportation in "very few exceptional cases" such as a known threat to an individual.
The Conservatives said Mr Blair was "rattled" while the Lib Dems argued the policy was probably unlawful.
The prime minister said the measure might not apply to foreigners who had been in the UK for a long time and only served a short jail term.
He said: "In the vast bulk of cases, as was explained, there will be an automatic presumption now to deport - and the vast bulk of those people will be deported," he said. "Those people, in my view, should be deported irrespective of any claim that they have that the country to which they are going back may not be safe.
"That is why it is important, if necessary, that we look at legislating to ensure that such an automatic presumption applies."
They should not be able to claim their home country was too unsafe generally, he said, pointing out people were now being deported to Iraq and Afghanistan.
Sir Andrew Green, from Migrationwatch UK, said he was "surprised" by Mr Blair's words but said he thought the current balance was wrong.
"Too much weight is being given to the possibility of someone suffering when they get home and too little weight is given to risk to British society," he said.