Lately even London Mayor Ken Livingstone, long Mr Blair's bete noir, was brought into the euro "big tent" recently when the group was given prime ministerial approval for the former left-winger to head its campaign in the capital.
His fellow Tory and former deputy prime minister Michael Heseltine told the same programme it was a mistake for Mr Blair to "hold back" on making the case for the euro.
And Liberal Democrat leader Charles Kennedy described a sense of "growing frustration" among euro supporters at the government's failure to offer leadership following last October's launch of the cross-party Britain in Europe campaign.
Big tent
Britain in Europe's launch saw Mr Blair, Chancellor Gordon Brown, Foreign Secretary Robin Cook, Mr Clarke, Mr Heseltine and Mr Kennedy on one platform in a bid to show that key figures of all mainstream parties were behind it.
Lately even London Mayor Ken Livingstone, long Mr Blair's bete noir, was brought into the euro "big tent" recently when the group was given prime ministerial approval for the former left-winger to head its campaign in the capital.
But behind the scenes of Britain in Europe's national launch last year, the film - The Battle for the Euro - reveals, there were disagreements over the government's approach.
Mr Kennedy disclosed that he was asked to tone down a passage in his speech which went too close to open support for the euro for Mr Blair's and Mr Brown's liking.
It was Mr Brown who had insisted, in a meeting weeks before the launch, that Britain in Europe must not argue openly for the euro, said Mr Kennedy.
The Lib Dem leader said: "The campaign itself was actually being told not really to campaign on the issue on which it had been founded, which is rather difficult for any group of political campaigners, and frustration then began to well up."
No follow-up
Mr Heseltine told the programme: "I think that was a mistake, as it has turned out.
"The real issue is the euro and I think that Tony Blair is in a position of being open to much criticism for the fact that he appears to be holding back."
Mr Clarke said that when the idea of Britain in Europe was first proposed, it
was designed as "the organisation that will be the Yes campaign" for a
referendum on euro entry.
He criticised the government for its unwillingness to set out the case for euro entry: "They are an indecisive lot, they're a pretty lightweight government.
"I mean, we got them on the platform for the launch of Britain in Europe, but they didn't follow up properly.
"If the official opposition are raising all these anti-euro arguments, I would expect the prime minister and the chancellor of the Exchequer to answer that, not to leave it to a middle-ranking minister for Europe, Keith Vaz."
In a statement issued on Friday, Britain in Europe said: "We are a historic coalition that embraces a wide range of opinions, united in a common campaign."
The Battle for the Euro is due to be broadcast on BBC2 at 19.25GMT on Sunday 17 December.