Even now, parties move on to war footing

Polling-day may still be 18 months away, but all three of Britain's main party leaders have already begun mobilising their forces for what could be the longest election campaign in history.

Gordon Brown's nationwide "recession tour" last week, against the backdrop of thousands of jobs disappearing on high streets and in car factories across the country, fuelled the sense that serious preparations for a poll have already begun.

David Cameron is itching to undertake a major shadow cabinet reshuffle to put the final line-up for the election in place, although this may be delayed for another week. Even Nick Clegg managed to reshuffle his team last week, declaring that he had put together the people he would take into the general election.

But it is the return of Alan Milburn, to chair Mr Brown's panel on social mobility, that represents the clearest signal that Britain has entered pre-election mode. The recall of the former Blairite arch-enemy, after Peter Mandelson was allowed back in October, is hugely significant; amid a crisis that could end his political career, even this Prime Minister is prepared to forgive and forget.

Barely six months ago, with his feud with the Prime Minister still simmering and dismayed at David Miliband's failure to challenge Mr Brown, Mr Milburn was expected to quit parliament for a business career. His outside interests already earn him at least £100,000 on top of his MP's salary.

However, since an initial approach during the Crewe by-election in May, the two men have been moving closer. Mr Milburn still sees weaknesses in the Prime Minister, but he is less anxious about Labour's chances than he was last summer. Social mobility is also a pet issue, one he sees as central to New Labour as it offers the opportunity to "grow the middle class" – and he helped to write a Brown speech on the subject in June.

Mr Milburn has also been planning a television programme on the relative achievements of his own classmates since they left school in the North-east more than 30 years ago.

"You have to be fair to Alan and say that this is an issue he has been particularly interested in," a Milburn ally said last night. "But I am very surprised that he has gone back into a Brown government.

"It is probably a combination of him being genuinely interested in the subject, but it also suits him in his business career to be seen as someone of substance who is still important in politics, who gets asked to do things.

"He also knows that, once again and against all the odds, Brown has become the only show in town. It isn't credible any more to be seen as someone who is sulking on the sidelines."

The work of setting out a policy platform while clearing overhanging government business continues this week. Tomorrow, ministers will host a "jobs summit" with business leaders, designed to help get 100,000 people back to work, and the following day they will launch their White Paper on social mobility, opening up access to the professions for people from deprived backgrounds. At some stage soon afterwards, Geoff Hoon must make the difficult announcement that Heathrow airport will be allowed its third runway.

Mr Cameron's Conservatives will not be far behind with a mobilisation operation that he hopes will begin in earnest with a long-delayed reshuffle. The leader's hands have been tied while he awaits the outcome of the parliamentary inquiry into party chairman Caroline Spelman's payments to her nanny. A decision is expected within the next two weeks, after the Standards & Privileges Committee has seen the report into her conduct.

A return for veteran former cabinet minister Ken Clarke remains on the cards, although speculation last week that he would be given Alan Duncan's job as shadow Business Secretary caused a backlash from the Tory grassroots. One alternative option is to give Mr Clarke a peerage, pitting him directly against Peter Mandelson at the Lords despatch box.

The Tory leader faces fierce resistance from the environmental community if he removes Peter Ainsworth from his Defra brief. Mr Ainsworth is among those tipped for the sack, but campaigners warn that sacking the well-respected MP would confirm fears that Mr Cameron has ditched his commitment to the environment.

The Conservative leader put his party on a war footing last night with a letter to candidates telling them to be prepared for an election at any time. Tory election campaign mailshots have been sent to 300,000 households, and a nationwide advertising campaign will be launched this week.

The leading businessman and philanthropist Stanley Fink has donated £1m to the Conservative Party and has been appointed party co-treasurer, with responsibility for building a general election fighting fund. Meanwhile, Samantha Cameron was given a favourable six-page profile in Vogue, in a sign that the party is pushing for more exposure for the Tory leader and his wife.

The battle will be joined as never before in the glossy magazines, as well as the cockpit of Parliament.

Who else might come back?

David Blunkett

Former home secretary forced to resign twice but was promised a return. There was speculation before Christmas that Blunkett, still regarded as a heavyweight, was holding out for a seat at the top table. He has praised Brown's handling of the economy in his newspaper column.

Odds: 7-4

Charles Clarke

Once the deadliest enemy of Brown but after Peter Mandelson's return he publicly buried the hatchet and backed the Prime Minister for the next election. Would welcome a return to the frontline, but perhaps in an advisory role.

Odds: 5-2

Stephen Byers

Like Milburn, another Blairite whose stinging criticism of Brown's first few months in office undermined the Prime Minister. Has cabinet experience but is not regarded as being in the same big league as Milburn or Clarke.

Odds: 33-1

John Reid

The PM's bitterest critic now has a full-time job as chairman of Celtic.

Fingers were pointed at Reid during the mini-challenge to Brown's leadership in September, as many of the rebels had links to him. Some would give shorter odds on hell freezing over, but then the same was once said of Mandelson.

Odds: 1,000-1