Steve Richards: Gordon Brown has built a big tent. But what happens if the weather turns nasty?

Gordon Brown opens the political season by giving an interview to the Daily Telegraph and recruiting two Conservative MPs to his progressive consensus. Soon David Cameron will run out of Tory backbenchers to put on his frontbench. They will be too busy working for Brown. In addition, Brown delivers a speech to those who work in the voluntary sector, a group wooed assiduously by Cameron in the past. He speaks of the need to make use of the widest range of experts, to rule from the centre ground and to end the old, tired slogans of previous political battles.

Mr Brown returns from his non-holiday even more determined to be the apolitical leader of the nation, the personification of consensus, the seeker after common ground. In doing so he aims to make life a nightmare for Cameron, in a consensual spirit of course.

Brown decided on his Prime Ministerial pre-election strategy several years ago. Conservative MPs and newspapers are wooed. Lines are kept open with the Liberal Democrats. Potentially awkward Blairites in the Labour party and the media get soothing attention. The focus is on policies with a moral dimension – such as gambling and those relating to public trust – or those that are practical, such as how to ensure domestic security.

In terms of the economy, the dividing line is between competence and the threat of Tory incompetence rather than a raging ideological debate. Issues such as inequality in Britain are part of the mix, but played down until there is more political space in which to act. Homage is paid to Blair's "reforms" of the public services, while more quietly, and yet necessarily, adjustments are made.

On its limited terms, the strategy is working. The Conservative MP Patrick Mercer, who was sacked by Cameron, now leaps to attention on behalf of Brown. He will advise Lord West, the former first Sea Lord who is now a member of the ministry of all the talents. Some ministers tell me that of all the non-Labour members recruited to the Brownite cause, Lord West is the most likely to join the party in the coming months. Other ministers have hopes still that the Conservative MP John Bercow will make the leap first. Bercow is a genuinely progressive liberal who has moved from the right out of principle rather than expediency, and who has also more recently shifted from being a devout eurosceptic to one who articulates the pro-European cause. Not surprisingly, Bercow has started to have his doubts about Cameron.

For now, Brown must make do with a third-way solution rather than an outright defection. Bercow remains a Tory while embarking on a project for Brown. Still, the symbolic potency of some Tories working willingly for Brown will be deeply unnerving for Cameron. And if the Conservative leader is not unnerved, he should be. Brown's big tent is starting to make Blair's seem like a puny strip of canvas on the top of a windswept cliff. Cameron had hoped the political traffic would be moving in his direction by now. Instead he loses a disillusioned deputy party treasurer and has two of his own MPs dancing happily to Brown's consensual tunes after already losing one to the new Prime Minister during the summer.

Mr Brown knows how to win elections. He was brought back to the fold before the 2005 campaign because Labour stumbled when he was exiled to the fringes. For more than a decade, he has turned around campaigns in Scotland and elsewhere. Now, for all the talk of the need for consensus, his every public word and deed is focussed on winning the next election, to achieve the space to act at last as a free agent, rather than one who rules on the basis of a manifesto drawn up by Blair.

Although the electoral mood is volatile, the polling evidence suggests that Brown is on course to achieve his liberating victory. A few months before he became leader, I pointed out in a column that while Brown's foes tormented him with what happened to James Callaghan, a Labour Prime Minister who lost an election, he could take comfort from the forgotten phase of John Major's career. Major took over from the long-serving Margaret Thatcher and won a fourth election with ease. Brown is achieving the same balance as Major, signalling change without breaking wholly with the past and at the same time confusing insecure political opponents into making mistakes.

But what followed after Major's election win in 1992 should act also as a warning for Brown. Major was so obsessed with winning an election he paid inadequate attention to what he would do once he had won. Brown will not make precisely the same mistake. As a tireless strategist, he probably knows the Queen's Speech he would like to deliver in 2025, let alone the legislative proposals after an election. Yet the manner of the victory, what is said and done now to bring it about, will shape what happens afterwards. Last Thursday I argued that Brown would be mistaken to call an autumn election on the grounds that he had potentially lethal loose ends to address before he could consider going to the country, Iraq, the NHS and Europe being three of them. There is another reason. An opportunistic rush to victory on the back of a few good polls would not be the authority-enhancing win required for the start of an inevitably tricky fourth term.

Fourth terms are potentially nightmarish terrain. Voters are much less tolerant. The media is capable of turning through boredom alone. MPs of the governing party can become complacently mutinous. There is a greater need for momentum and direction than there is in a first term when a new government wallows in undeserved goodwill.

What matters at least as much as when Brown makes his electoral move is that, having done so, he has the space to make a difference if he wins. There is no point winning only to find that there are so many contradictory forces in the bulging big tent that it is impossible to act without all hell breaking loose.

There is still a huge progressive agenda out there, the absurd inequality of incomes, the inadequate level of investment in parts of Britain's creaking infrastructure, the need for universally high levels of public services enjoyed in other parts of Europe, the genuine empowerment of local communities, a more innovative and enlightened foreign policy. No doubt Brown finds the support of everyone from Alan Greenspan and Tory MPs to JK Rowling extremely useful, but can they all be deployed to bring about the sweeping changes needed in Britain?

In deciding the terms of the next election battle and its timing, Brown would be well advised to recall Major's hellish experience after his extraordinary triumph in 1992. To be sure of avoiding similar nightmares, Brown must seek a progressive consensus for a well- defined purpose. We need to hear much more about the purpose to make any victory worthwhile.

s.richards@independent.co.uk