In an interview with The Independent, Philip Gould, Tony Blair's pollster and strategist, said he wanted Labour and the Lib Dems to form a "progressive coalition" to dominate the 21st century and push the Tories to the margins of British politics. Although he said Labour could achieve this goal on its own, Mr Gould said: "My opinion is that the two progressive traditions can be joined. Ideally, they would be."
In a book published next week, Mr Gould calls for Labour and the Lib Dems to "converge, effectively becoming one party".
While Labour could marginalise the Lib Dems, he writes, "the better course would be for Liberalism and Labourism to unite".
His comments provoked anger last night on the Labour left, which has always suspected the New Labour "project" involves a merger with the Lib Dems - a claim denied by Mr Blair. Left-wingers were also worried by Mr Gould's call for the new coalition to appeal to Britain's "new middle- class politics". Mr Gould said in the interview: "The middle class has to be at the centre of the coalition, because you cannot form a government unless you have the support of the middle class."
Alan Simpson, Labour MP for Nottingham South, said last night that if Mr Blair tried to merge with the Lib Dems, the trade unions and Labour left would form a breakaway party.
"It would probably be a very good trigger point for the formation of a different party, which had its roots in the trade union movement."
Mr Gould's comments will increase the pressure on Mr Ashdown, who is under fire from Lib Dem critics who fear the party will be "swallowed up" by Labour. A cabinet committee including Labour ministers and senior Lib Dems meets today.
Gould interview, page 12