Mr Blair was challenged over whether the Government's five-year asylum and immigration plan, published this week, would lead to a rise or fall in net immigration.
He said: "The numbers probably will fall because those people who are coming in, abusing the system or who aren't covered by the restrictions, won't be able to settle here."
The Prime Minister's forecast contradicted the Home Secretary, Charles Clarke, who said on Monday the proposals were unlikely to greatly affect overall migrant numbers.
Under the plans, only highly skilled workers who speak English and pass a "Britishness test" will be allowed to settle permanently in the UK. Low skilled migrants will be permitted to enter for fixed periods and have no right to settle.
Mr Blair ridiculed Tory proposals, which include an annual cap on immigrants and off-shore processing. But Mr Howard produced a letter from the Prime Minister to the President of the European Council in 2003 offering to discuss the idea of sending people seeking asylum in EU countries to a "transit processing centre" outside the European nations.
The Tories returned to the impact of the expansion of the European Union on 1 May last year. New figures showed that 1,029,000 people from the eight new Eastern European members visited Britain in the first eight months after accession with 92,000 intending to stay for more than three months. That compared with an initial Government prediction that expansion of the EU could lead to net migration of up to 13,000.
wMigrationwatch, the right-wing immigration think-tank, said in a report last night that there had been a major trend of white families moving out of London to the regions, while large numbers of ethnic minorities arrived in the capital from overseas.Reuse content