The deputy Prime Minister told a BBC Radio 5 phone-in: "I know people find this difficult to believe, but I know we are gaining from the European partnership, and I know that to be outside it would be a disaster. You say rightly the economy is doing very well but I tell you, if we were in fact to prejudice Britain's position in Europe, you would find a very different situation."
The Labour leader said at a What the Papers Say award ceremony, in London: "The Labour Party is clear that we do not want to leave the EU. Formally, the Tory party agree. It is increasingly unclear, however, whether that will hold."
Mr Heseltine's acknowledgement of the risks involved in withdrawal suggests a growing fear on the Tory left that the Euro-sceptics are setting the pace of policy. But as with Lord Howe's warning on Thursday - that the former deputy Prime Minister could not support a party that was "hostile" to the principle of a single currency - Mr Heseltine appeared to be warning that he is not going to surrender without a bitter fight.
Mr Blair said: "They are irreversibly divided on Europe because a significant part of the Tory party want to withdraw from the EU. No serious part of the Labour Party wants to withdraw."
On the single currency, the Labour leader said the options had to remain open for a "hard-headed assessment of Britain's national interest"; something that was also supposed to be the Government's position.
Mr Blair said that if that policy was being changed, then the Prime Minister "should spit it out ... But he should not carry on having it both ways, two faces, one in either direction. Inconsistent, unreliable, untrustworthy".
The image of a two-faced Mr Major is expected to be the theme of Labour's latest pre-election poster campaign, to be launched by deputy leader, John Prescott, in Birmingham today.
But Paddy Ashdown, the Liberal Democrats' leader, said last night: "The Conservative and Labour parties both treat the single currency like an embarrassing relative no one wants to mention ... We believe that being part of a successful single currency would give Britain lower interest rates and lower inflation, and staying out would give Britain less inward investment and less influence."Reuse content