As befits the unveiling of a truly historic occasion, as the organisers kept describing it, the venue was the mega-screen Imax cinema on London's South Bank.

The previous day the chief attraction had been Destiny in Space, which took the audience "flying over the surfaces of Venus and Mars", according to the cinema's programme. The day after it would be Into the Deep - "swim with the sharks, play with the sea-lions".

But on Thursday, for one day only, the main feature was Britain in Europe - an epic tale of passions inflamed and one country's date with destiny.

By invitation only

The likes of Peter Mandelson and Lord (Geoffrey) Howe hob-nobbed at the launch

As with any premiere, the audience was strictly by invitation only, and included faces from the past and present all connected by their pro-European leanings: Peter Mandelson, Edwina Currie, Richard Branson, Leon Brittan, Trevor Phillips, Ted Heath, Shirley (now Lady) Williams, Lords Jenkins, Howe and Hollick.

In keeping with the cinematic surroundings, the main feature was preceded by a short, complete with Pearl & Dean-style thumping music. Yes, it was the Britain in Europe (BiE) promo video, in which assorted pro-Europeans from the worlds of industry and politics told us about the benefits being in the EU and the euro.

Finally, what everyone had been waiting so long for - months, if you counted from the time BiE originally intended to launch itself - began. Colin (Lord) Marshall, chairman not only of Britain in Europe but also of British Airways, ascended the podium to kick off the proceedings.

Suddenly it turned into the Oscars, with Sir Colin thanking everyone he could think of - the audience, the press, people looking in on the Internet, the owners of the Imax - for making the event possible.

Also fulsomely thanked were, entering stage left as he introduced them, the stars: Michael Heseltine, Tony Blair, Ken Clarke, Gordon Brown, Charles Kennedy and Robin Cook.

They crowded onto the small stage, a rainbow coalition of pro-Europeans clearly united behind BiE's message.

What precisely that message is was less clear. The prime minister was the first up to speak, arguing the case for, well, not for the euro exactly, or even at all, but for the European Union.

Shared mission

So far as the single currency went, Mr Blair declared that "in principle" if it succeeded he was in favour of joining. Yet not even the most Eurosceptic Tory has ever accused Mr Blair of wishing to join the euro if it were a failure.

Next came Michael Heseltine. The former deputy prime minister came closer to the heart of the matter, warning of the dangers of staying outside the euro.

Perhaps predictably, it was Ken Clarke who said what everyone else was trying not to mention

Charles Kennedy, leader of the Liberal Democrats, the only main party whole-heartedly committed to signing up to the single currency, was next.

The euro merited not a single mention in his speech. Instead he talked of their "shared mission", which was: "To explain why Britain is in Europe. To explain that it is good for British business. Good for British jobs. Good for British people. So it is patriotic to be pro-European."

As ever it was Ken Clarke, during the following Q&A session, who came out with what everyone was really thinking.

"Everyone who's joined this campaign has joined it in principle because they're in favour of joining the single currency," he said, breezily breaking the event's unofficial Don't Mention the Euro rule.

For a barely perceptible millisecond, the smiles on the faces of Tony Blair and Gordon Brown, sitting either side of him on the platform, froze.