If a week is a long time in politics, the bad news for Gordon Brown is that he is only halfway through this one.

It began with a Sunday morning TV appearance in which the Prime Minister was determined to deliver a clear message — he wasn’t about to quit. Indeed, in addition to rescuing the economy he was also going to clean up the entire political system.

Four turbulent days on, his pre-emptive relaunch has foundered amid signs of a fully fledged ministerial mutiny. Gravely weakened and apparently rudderless, Mr Brown is grimly determined to weather the storm.

Sunday’s questions in the BBC’s television studios were tough. Did no part of him feel that he was the problem? That his party would do better without him? That it was “time to stand aside and let Alan Johnson or whoever it is come in and have a go”?

In reply he delivered his prepared script that only he could steer the economy from recession and clean up a Parliament that had offended his “Presbyterian conscience”.

The reference to his background as the son of a Church of Scotland minister was a less than subtle attempt to rise above the expenses scandal and remind voters of his personal probity.

Spending a rare weekend at his Edinburgh home with his wife, Maggie, Alistair Darling might have allowed himself a snort of derision. He had read that morning that Mr Brown was preparing to replace him with Ed Balls in a reshuffle on Friday, the day after the elections, when Mr Brown would face the greatest threat from his party.

The Chancellor has been fighting off Mr Balls’s claims on his job ever since he was given it almost two years ago. Speculation that Mr Brown would promote his economic guru to No 11 had, until recently, receded after Mr Balls was damaged by the Damian McBride affair. Once the expenses scandal broke, however, it was Mr Darling’s turn to see his reputation tarnished as he fought off allegations that he had “flipped” his second home to maximise his Commons allowance. In addition, Mr Darling was aware he was being marginalised within No 10 by a new alliance between Mr Balls and Lord Mandelson. Mr Darling’s aides believed that the Business Secretary — increasingly the fulcrum of the Brown Government — could not be relied upon to defend him.

Once the Prime Minister turned his attention to his “relaunch reshuffle” last week it seemed clear that Lord Mandelson had given a Blairite blessing to the promotion of Mr Balls.

As Mr Darling and his allies sought to manage the fallout from the Sunday Times leak, they received news that they were about to be hit by another series of revelations over his expenses. That afternoon The Daily Telegraph sent the Chancellor’s aides a detailed list of questions on his claims for his second home allowance for the time he had moved into his grace-and-favour flat in Downing Street.

No 10 watched anxiously as the Chancellor’s team struggled to close the story down — not least because Mr Brown had been booked into a round of interviews for Monday.

The issue of Mr Darling’s expenses predictably dominated Monday’s interviews, which had been intended to showcase Mr Brown’s proposals for constitutional reform. The Prime Minister faced an almost impossible task of keeping open his options on the reshuffle while defending his friend from a media onslaught.

Assured that the Telegraph’s headline, which claimed that Mr Darling had billed taxpayers for “two homes at the same time”, was inaccurate, Mr Brown said there was “no foundation” in it. Mr Darling’s officials must have winced. Before them, in minute detail, were details that showed that the text of the article — if not the headline — was broadly correct: he had indeed claimed for a service charge on a property when it was let.

Within an hour of Mr Brown’s full support, Mr Darling was forced to endure the embarrassment of issuing an apology and offering repayment. When Mr Brown started using the past tense to describe his tenure as Chancellor it seemed he was all but finished at the Treasury.

But where could Mr Brown put his friend, to whom he owed an enormous debt? David Miliband, in the Foreign and Commonwealth Office, also read Sunday’s papers with acute interest. Whatever else happened, he decided on Monday that he was not going to be demoted simply to facilitate the promotion of his political enemy, Mr Balls. As he and other senior ministers took their seats the next morning around the Cabinet table, it was becoming hard for them to look each other in the eye as each made their own calculations about the reshuffle. Contrary to claims that the Prime Minister delivered a commanding performance, one senior minister told friends that Mr Brown “only just got through” the Cabinet as he outlined his plans for constitutional reform.

Jacqui Smith, the Home Secretary, emerged from No 10 to learn that news of her departure from the Government had been leaked. That added to the sense of gathering crisis.

No 10 immediately suspected Hazel Blears of feeding the media this and other stories of ministers standing down in an attempt at sabotage. Ms Blears was summoned to explain herself in Downing Street that evening. Meanwhile, other Cabinet ministers were openly defying Mr Brown. Mr Miliband fired a warning shot over the Prime Minister’s bows, insisting that he wanted to stay at the Foreign Office for at least “four more years”.

Inside the No 10 bunker, Mr Brown has been surrounded by comfort blankets — Lord Mandelson, Mr Balls, Ed Miliband and Douglas Alexander, trusted confidants of old.

When Mr Brown began his preparations for Prime Minister’s Questions he could be forgiven for finding it hard to muster his usual concentration. The cast of officials assembled in the Cabinet Room — led by Jeremy Heywood, his permanent secretary, and Michael Ellam, his official spokesman — to begin briefing Mr Brown. But the Prime Minister had to break off to make calls and hold hurried meetings.

Next door Mr Darling was at a leaving party for aides in No 11. When news came that Mr Brown had sent for him, guests wondered whether the gathering might become a wake for the man himself. Reports vary about what they discussed in their five minutes behind closed doors. Some insist it was a routine discussion about PMQs, others that it was Mr Brown’s opening of negotiations about the price of Mr Darling’s exit.

Yesterday morning Mr Brown resumed his preparations for PMQs. Soon after 9am they were interrupted by news that Ms Blears had returned to Downing Street — this time uninvited — and wanted to see the Prime Minister. Her resignation, a calculated revenge, was received with cool fury but little surprise. Despite the usual courteous exchange of letters Mr Brown’s allies fully expect Ms Blears to denounce him as soon as the polling booths close tomorrow night.

Last night he was aiming to steer somehow to the haven of next week. Listing badly, his premiership is not, yet, sunk.

What may happen next: four scenarios

• Gordon Brown announces he is stepping down at the end of the summer after a disaster in local and European elections. A leadership contest is held in September. The new leader is crowned at Labour’s conference and announces that he will hold a general election in the first week in November.

• He is forced out before recess, but senior Cabinet figures, including Alan Johnson, are tainted. This leads others, including Ed Balls, to throw their hats in the ring to succeed him, leading to a bloody leadership battle. The decision is announced at conference, but attempts to heal the party wounds fail. Divided, they lose just as badly as they would have done with Gordon Brown in charge.

• The damaged Prime Minister limps on, believing the public will reward him as the green shoots of recovery are just around the corner. Labour gives up the fight and donors desert, with the unions providing almost all the funding.

• He calls an early election for the second week in October, denying opponents the chance to challenge him. The move wrongfoots party members — and David Cameron — who are surprised he has taken such a bold decision.

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