A defiant PM will make it clear in Brighton that quitting is not an option

It will be the last gathering of the Labour tribe before the General Election, quite possibly their last conference as the party of government for several years. And, for Gordon Brown, it will begin in church.

As the son of a clergyman, the Prime Minister will know that, when he takes his pew in Brighton this morning, he should give thanks for what his team believes was a remarkably successful week on the world stage. But he may also be tempted to throw himself on the mercy of the Lord – or at least offer a silent prayer for salvation. Brighton 2009 threatens to become a requiem for Mr Brown's political career.

In response to fears that he is nearing the end of his time in power, he will offer a pledge to go on and on. He will use the week to send a message that he is going nowhere – and to set out Labour's "governing purpose" for the next five years.

Cabinet ministers each day will set out the "big choice" voters face at the next election, culminating in the publication of a draft manifesto: "The Choice for Britain". Strategists said the next election will not be a referendum on the Government but a choice between "Labour's programme to help the many" versus the Conservatives' agenda to "cut people adrift" – which will be seen as the PM sticking to the Labour investment versus Tory cuts argument.

The defiant focus on his own agenda echoes the response of former Labour prime minister Harold Wilson to suggestions that his own colleagues were plotting against him. "I know what's going on," he declared in 1969. "I'm going on." Just months later, he was booted out.

Writing in the foreword of the draft document, Mr Brown will say: "We are fighting for a better future for our country. In the next election campaign, the choices will be starker than ever. To win the fight, we must not only defend our record and achievements: we must show how we are driving forward to meet new challenges.

"We are setting out plans for a post-crisis economy. We are setting out plans for a post-crisis society. And we are also setting out plans for a post-crisis politics – showing how we intend to reform our democratic institutions, rebuilding trust in politics and public life."

His rallying cry will not, it appears, be interrupted by another grubby scramble to prevent a challenge to his leadership this week – although a putsch in October or January has not yet been ruled out. The perpetual opposition appears becalmed – not by admiration for Mr Brown's performance in adversity, but by a resignation that they are saddled with a leader who will lead them to certain defeat.

The sense of doom is reflected in the behaviour of Mr Brown's Government: in a week, the Prime Minister has lost two colleagues, while another clings on by her fingernails.

Lady Vadera's departure, for a key role at the G20, was a blow to Mr Brown, regardless of its billing as a promotion for the peer. However, insiders said that, while her writ ran through Downing Street, she clashed with the Chancellor, Alistair Darling, and the Business Secretary, Lord Mandelson, in their departments.

But The Independent on Sunday has learnt that another member of Mr Brown's inner circle is planning to follow trusted advisers such as Damian McBride out of the door. Sue Nye, his gatekeeper for more than a decade and head of government relations, is understood to want a "change of scenery" and a "bit of distance" from the troubled surroundings of No 10. She is being lined up for a seat in the House of Lords in the next peerages list – which would see her leave Mr Brown's side before the next election.

A source said she was not planning an exit "under duress", but there were suggestions that Ms Nye was increasingly irritated at the growing influence of Kirsty McNeill, Mr Brown's former speechwriter, who was recently appointed Downing Street's head of external affairs.

Mr Brown's global standing was enhanced by his active role during the UN General Assembly and the G20 summit in Pittsburgh; it was embellished by the six-page Newsweek feature "My Plan to Save the World", and a World Statesman of the Year award presented by Henry Kissinger.

Hence the furious response to the British media's decision to concentrate their coverage of the UN summit on the "snub" delivered by President Obama in response to British efforts to arrange a one-to-one meeting with Mr Brown. The uncomfortable relations with the press, which continued on the plane home to London, underlined his exasperation with British journalists – and the degree to which he has "lost" the crucial media battle.

No matter. The Brown camp is convinced that, with the economy in recovery, by next spring the Government will have a story to tell that cannot be distorted: not only was Brown the politician who steered the UK out of recession, but he was also the man investing in recovery when David Cameron was urging austerity.

The prospect will be some comfort during a difficult week when the Government will face attacks from the right and left, from former colleagues, union members, party faithful and, ultimately, apathy. His closest allies will loyally offer their public support as pressure builds against him. But, in the longer term, Mr Brown may need greater protection from the potential challengers lining up to take his place.

Alan Johnson has issued his familiar claim that he has no ambition to be Labour leader, but he remains the favoured choice of Labour members – not only Charles Clarke – who believe the party can only be saved from annihilation by replacing Mr Brown before the next election. More significantly, the younger, would-be heirs to a post-election Labour Party are beginning to display their independence.

In an interview with the IoS today, Foreign Secretary David Miliband sets out his "pitch" for the future of the party – and challenges the Prime Minister to show he has "a vision for the future as well as... a proper assessment of the last 12 years".

Ed Balls yesterday exhorted Labour to fight for a fourth term in office. But, in a show of frustration at Mr Brown's regular comments on popular television shows, he added: "They [the public] want to know that the Prime Minister is being prime ministerial."

Intriguingly, however, an older colleague is emerging as a potential inheritor of the post-Brown spoils. Mr Darling, the man who chatted happily with journalists on the plane home from the US, while Mr Brown steamed at the front, is known to be frustrated at the Prime Minister's continued interference in Treasury business. But his hand has been strengthened by Lady Vadera's departure and, ultimately, he stands to gain as much as Mr Brown from the "recovery dividend" if the economy progresses as No 10 hopes.

The unassuming Chancellor is unlikely to throw down a challenge to the Prime Minister when he speaks to conference tomorrow, in the way Mr Brown's barnstorming addresses traditionally threw down the gauntlet to Tony Blair. But, in the long run, Mr Darling may have the most to gain from any recovery, and his colleague's inability to take political advantage of it.

How the prime minister's inner circle is shrinking

Sue Nye

Leaving date: Shortly?

Ms Nye, 54, has been Gordon Brown's gatekeeper for more than a decade and is now also head of government relations. She is married to former BBC chief Gavyn Davies, and their children, Ben and Rosie, were pageboy and bridesmaid at the Browns' wedding in 2000.

Shriti Vadera

Leaving: Next month

Mr Brown's closest adviser after Lord Mandelson, former banker Baroness Vadera, 46, has a desk in No 10's "war room". She leaves the Government next month to advise the G20 on international finance. Most famous for saying last January that she could see "green shoots" in the economy.

Damian McBride

Left: April 2009

Mr McBride, a long-serving press officer, was turfed out of No 10 in shame after planning, by email, a smear campaign of senior Tories. The 35-year-old, nicknamed "McPoison", is close friends with Ed Balls. He now works as a community manager at a school in Finchley, north London.

Stephen Carter

Left: October 2008

The former Ofcom chief was drafted by Mr Brown in January 2008 as strategy chief to professionalise Downing Street. This upset the Brownite old guard and by autumn he was shifted to the Lords and a ministerial job. Lord Carter, 45, resigned in June to return to the private sector.

Spencer Livermore

Left: March 2008

The former director of political strategy, 34, quit after being blamed for the "election that never was" fiasco of October 2007. He left for a job at Saatchi & Saatchi and is now at PR firm Blue Rubicon. Lord Mandelson tried to persuade him to return as chief of staff – but he refused.

What to expect at the party gathering: Protests, policy, and young pretenders

Policies

Not too many of these, partly because the spending limitations have reduced room for innovation and partly because no one wants to give their best ideas away too soon before an election. Nevertheless, Labour promises all Cabinet ministers will set out the "big choice" that voters face at the next election, culminating in the publication of a draft manifesto: "The Choice for Britain" by the end of the week. Gordon Brown has already grabbed the juiciest new idea so far, making it known that he will ensure suspected cancer patients are guaranteed a specialist screening within a week. What an accommodating Health Secretary that Andy Burnham is.

Challenges

The habitual shows of dissent begin early, when the conference launch rally is expected to be overshadowed by a protest outside – from postal workers, rail staff, teachers and civil service workers. The big issue is the impact of recession on their members – the spending reductions, job cuts and soaring unemployment. It will dominate the week, on the floor of the conference centre and in fringe meetings around Brighton. "Trade unionists from around the country will be gathering in Brighton to tell the Labour government that we are determined to defend jobs, and that working-class people should not pay the price of the economic crisis," explains the RMT. At least they aren't asking for a new leader.

Who to watch

Mr Brown is accustomed to keeping an eye on the behaviour of his Cabinet colleagues, during their podium appearances, but some of the most dangerous performances could take place during the "unofficial conference". Jon Cruddas, a former Downing Street staffer, has developed into a convincing critic from the left of the party, while James Purnell has become a standard-bearer for the Blairites since he quit the Cabinet in the summer. Both appear tonight at the Fabian Society meeting (ominously entitled "Next Labour") which has become a key rallying point for critics of the Blairite regime. Charles Clarke, an increasingly shrill Brown opponent, will debate the case for a "progressive coalition" at another Fabian fringe tomorrow.

Contenders

David Miliband remains the Man Most Likely, despite past reluctance to take the plunge – and despite his misfortune with a banana at last year's conference. The Foreign Secretary hints at making his "pitch" in the IoS today, but his podium speech on "Britain in the World" on Thursday will give an idea of his appetite for any challenge. He will rehearse his pitch during an Institute for Public Policy fringe called "New Labour, Dead or Alive", on Tuesday. On the same day, Alan Johnson will get his annual opportunity to rule out a challenge, but his speech – which already promises to be a populist one – will at least test the water. Alistair Darling promises to be one of the most fascinating contributors, not least because he will be able to offer something more than the funereal outlook of last year. He cannot expect to deliver the type of weighty address favoured by Mr Brown when he was Chancellor, but Mr Darling could at least destabilise the PM – if he chose to do so – by seizing a share of the credit for the more promising economic outlook.