Shadow home secretary David Davis made the attack after the premier insisted British business had benefited "very substantially" from immigration over the last decade.

Mr Brown pointed out that gross domestic product per head had risen dramatically since 1997, from £13,900 then to £22,840 in the last year.

The PM appeared to reject a suggestion by an influential House of Lords committee that immigration levels should be capped, noting that such a move could only apply to those coming from outside the EU.

"Most people who are proposing a cap are proposing a cap of only 20% of possible migrants into this country," Mr Brown said. "And of course many of these people are the highly skilled workers who are important to the economy.

But Tory Mr Davis said of Mr Brown's 20% figure: "The Prime Minister is in denial. His minister's previous assertions about this have been shown to be bogus. It's either a sign of desperation or pure lack of grasp that he is repeating them."

Tory leader David Cameron said: "We want people to work here and come to Britain.

"The problem with the Government is that they absolutely refuse to set any sort of limit on immigration."

He added: "If you want to control immigration you have to control that bit of immigration you are able to control. It's still possible to control non-EU immigration."

The peers' report dismissed the Government's claim that immigration is good for the economy and called on ministers to set an "explicit target range" for the number of arrivals.http://www.parliament.uk/index.cfm(Parliament)