The Government has described Boris Johnson's proposal for an amnesty for illegal immigrants as "naive".

The Mayor of London reopened the debate over how to deal with hundreds of thousands of people working illegally in the UK, insisting that simply deporting them was "just not going to happen".

He said that allowing long-term illegal immigrants to earn the right to stay in Britain would see "hugely increased" tax revenues.

But Immigration minister Phil Woolas said the move could lead to more people being exploited by traffickers.

Mr Woolas said: "I think this is naive of the Mayor. His comments might start with the best of intentions but will lead to more people traffickers making more money and exploiting more vulnerable individuals.

"The UK Border Agency is committed to stopping illegal migration. We are putting in place the biggest shake up of the immigration system for 45 years and we are seeing the results of this. We are putting more resources into expelling foreign law breakers and last year we removed one person every eight minutes."

Mr Johnson and Tory leader David Cameron also clashed on the issue of an amnesty during his campaign for City Hall in April.

Mr Cameron was quick to express his disagreement, saying: "The problem with amnesties is that they just store up another for the future, as people expect another one."

Of the 700,000 illegal immigrants thought to be in the UK, about 400,000 are in London.

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