Steve Richards: This is the most dangerous week in the PM's career

Stand by for the most exciting and unpredictable few days in British politics for years. Yesterday the Home Secretary announced her resignation and three Labour MPs joined the growing army standing down at the next election. Normally such developments in a single day would be tumultuous. They are small beer compared with what is coming next.

Tomorrow the voters go to the polls for the local and European elections. The results of the local elections are declared on Friday. The outcome of the European poll is announced on Sunday. In between the two, or immediately afterwards, Gordon Brown will attempt to reshuffle his Cabinet in a desperate attempt to signal a fresh start. Given the depths of unpopularity to which Labour will sink over the next few days, the ministerial changes will have to be dramatic to counter the tidal wave of gloom that already engulfs Brown's party.

It is the reshuffle that is the most highly charged element of the sequence. Even the timing is strangely complex. Should it take place on Friday or Monday? Bizarrely, the decision is shaped partly by the fact that Brown and his entourage are heading to Normandy on Saturday for the D-Day commemorations. They cannot get out of that one. They see attractions in reshuffling before the weekend, but what if the changes go wrong as they often do? They might have to head for France in the midst of chaos.

The election results will be an important snapshot of public opinion. But they are broadly predictable. The focus will be on the scale of Labour's plight, the degree to which the Conservatives are moving forward, the precise impact of the Liberal Democrats and on the rise of the smaller parties.

After which, in a newly bleak electoral landscape, Brown will make his moves. The most important and fascinating question of the lot is whether he makes Ed Balls his chancellor. The two close allies have talked about the prospect for years. Brown considered making Balls chancellor when he became Prime Minister in 2007 even though Balls had not, at that point, been a cabinet minister. Now he has the chance to make the appointment and yet he might not be in a strong enough position to do so. In the aftermath of the elections, Brown will be deploying the mighty powers of prime ministerial patronage in a position of extreme weakness.

Balls is best qualified for the job in the Treasury by a wide margin. He is an economist who, one way or another, has been at the heart of economic policy-making since the early 1990s. Brown trusts him and values his judgement on every element of economic policy. He is also loathed by some of the noisiest internal dissenters as the closest member of the Brownite entourage. Balls's enemies have been working away in the media in recent days, making a series of pre-emptive strikes. Ironically their main accusation is that Balls is a divisive figure, not least because of his briefings in the media. A strong prime minister would normally brush such concerns to one side. Will Brown be in a position to do so? The fate of Balls will be an illuminating test of Brown's remaining authority.

Then there is the even bigger and related question. Will Brown be able to survive as Prime Minister if Labour's ratings are at the lower end of the already pessimistic expectations? Again, no one knows for sure, although most Labour MPs I speak to refer to a sense of melancholic paralysis rather than energetic insurrection. The expenses saga has drained their appetite for politics. Some of them even want an early election to get it over with as soon as possible, proving that in the current madness, some turkeys would vote for Christmas.

This is a very different situation from the fall of Margaret Thatcher when MPs rebelled against her in a bid to save their seats. Some MPs on both sides are past caring at the moment. But that could change too. Certainly there are some Labour plotters around, mostly those associated with constitutional reform who see Alan Johnson as a leader who could unlock doors and form a progressive alliance with the Liberal Democrats. But will they get very far? Brown's internal opponents have proved to be hopeless plotters over the years.

Within No 10 they accept that this is the most dangerous week in the Prime Minister's turbulent political career. They plan for a reshuffle and have announcements to make on the economy and the constitution. What will be the context in which they are announced? The outcome of the last three elections was predictable. Now, from hour to hour, no one knows quite what will happen next.