In the current febrile state of British politics, an issue that seems to boost a leader can suddenly become the source of his gloom. Senior Labour figures are still getting over their dance with an early election, the joyful jigs turning swiftly into a paralysing hangover. Now some Conservatives take to the dancefloor with an upbeat verve as Europe becomes a melodious issue for them once more.
This is the policy area that gets a lot of them going and, as a happy coincidence, aligns their party with the most powerful newspapers in the land. As an even more gratifying bonus, the Conservatives can make their case on the basis of 'trust' – the great simplistic cliché of our times. With heads held high, they claim that Labour promised a referendum on the EU constitution and is therefore obliged to offer one now.
In the same way that, for a time, the early election story terrified the Conservatives, the related issues of Europe and the referendum privately worries senior ministers. As one of them put it to me in relation to the persistent prominence of the referendum story: "I suppose it could be even worse but I assumed that, after we negotiated all the opt-outs last summer, we would be in a much better position over this."
The Government led by Gordon Brown never knowingly under- worries. It was the same under Tony Blair. "Oh my God, what have we done wrong now and how do we get out of the mess?" has tended to be the mood in Downing Street since 1997, whether Labour was 20 points ahead in the polls or well behind. But, as the Tories worried needlessly about the election story, Labour has cause to be more bullish about Europe. At the same time, it is the Tories who should be worried about the direction in which the debate on Europe is heading.
There are obvious tactical reasons why Mr Cameron faces difficulties. Already, a significant number of Conservative MPs are calling for a pledge to hold a referendum on the revised treaty at the next election, even if the agreement has been ratified across Europe. No wonder Mr Cameron and William Hague are evasive on this convoluted demand. Even if Britain wanted to cling on as a member of the EU, in such circumstances the rest of Europe would have every right to tell us to leave (presumably a new Conservative government would campaign for a 'no' vote against a ratified treaty, threatening to cause chaos).
Already, other EU members despair of Britain's adolescent behaviour, its semi-detached posturing. Such a proposal from the Conservatives in a 2009 election would be the final straw. Mr Cameron probably recognises that this would be a move too far but, if he accepts the treaty after ratification, he risks alienating that section of the party which regards Europe as the greatest menace of the lot.
The Conservatives also have a broader problem. Of all the recent changes in Europe, this is the one they should be supporting. The treaty contains relatively minor reforms made necessary as a result of enlargement. Here is Margaret Thatcher in her famous Bruges speech, the address that heightened the Euro-sceptic fervour in her party. It was the shrill tone that roused the passions of her ardent followers, rather than much of the substance. Her section on the wider Europe was modest and beyond dispute. "We must never forget that, east of the Iron Curtain, peoples who once enjoyed a full share of European culture, freedom and identity have been cut off from their roots," she said.
Now the peoples have got their freedom and identity as members of the EU. Lady Thatcher and other Tory MPs argued during the debates over Maastricht in the 1990s that the focus should be on enlargement and not a Franco-German project that sought sweeping integration. They have got their way, as they did over Britain's refusal to join the euro. Enlargement makes a Franco-German conspiracy impossible. The Tory Euro-sceptics should be raising a glass over this latest treaty, rather than spitting blood once more.
They should then be raising another glass to toast the fact that it is the British parliament that will be deciding whether to ratify the treaty. Here again is Margaret Thatcher in her also famous final statement to the Commons as Prime Minister, after the Rome summit in the autumn of 1991. When asked to support more powers for the European parliament, the EC and the Council of Ministers she shrieked: "No, no, no". Instead, she wanted power to reside in the British parliament.
At a time when it is fashionable in all the main parties to argue that parliament should matter more, this is hardly the moment to undermine its effectiveness by calling a referendum on a treaty of less significance compared with several others passed in recent years.
Beyond some parts of the media, I detect no great enthusiasm for a referendum, no overwhelming desire among voters to debate whether Britain's opt-in over crime policy is less of an opt-out than it seems. The great propagandists at the mighty Euro-sceptic newspapers have failed to generate much excitement so far and their failure is not down to a lack of effort. I never underestimate the power of British newspapers but I sense it was significant that The Sun's week-long campaign during the Labour Party conference, calling for a referendum, made the newspaper look silly rather than the fearful ministers who were terrified of its possible impact.
Yesterday's exchanges in the Commons showed how Mr Brown plans to move on from the current stifling debate. On one level, his statement was another depressing example of a prime ministerial speech with one essential message: "Europe is awful but, don't worry, we don't have to play along with it". Mr Brown highlighted the vetoes, the safeguards, the opt-outs and the opt-ins as if he was dealing with the equivalent of the plague. More hopefully, he looked beyond the treaty to a fresh agenda.
In this he was astute. The agenda outlined for the next decade by Mr Brown – in relation to making Europe more competitive, taking action on the environment and global poverty – is much less likely to be contaminated by Euro-madness and could even command a degree of cross-party support.
Mr Brown will be able to navigate his way through this treaty. I recall the frenzy among some Conservatives in the build-up to the Amsterdam Treaty. It was so intense that a pathetic John Major pleaded with them during the 1997 election not to "tie my hands" in advance of the summit. Consequently, Tony Blair signed up to Amsterdam and the fuss soon subsided. The fuss will subside over this treaty by the time of the election. Yet it will not have done so in the minds of some Tory MPs. That is why Mr Cameron should be worried as he dances in apparent joyful harmony with voters and Rupert Murdoch.