What happens now?

What happens when the post of first minister becomes vacant is laid down in the Scotland Act, the legislation that governs how Scotland's devolved parliament operates.

In the event of a vacancy, the presiding officer of the parliament, Sir David Steel, has to appoint someone as acting first minister until the Scottish Parliament elects a successor.

Jim Wallace, the Deputy First Minister and leader of the Scottish Liberal Democrats, has taken this role temporarily.

He did the job earlier in 2000 when Mr Dewar entered hospital for major heart surgery.

But he will only be able to play this role for a month. The Scotland Act requires the parliament to elect a new first minister within 28 days of a vacancy arising.

This election will be conducted under the same rules as the contest that occurred last year between Donald Dewar and Alex Salmond, then leader of the Scottish National Party.

Minority party

The SNP could nominate its new leader, John Swinney, for the post, but facing a Labour/Liberal Democrat majority he has no chance of being elected.

Equally, Jim Wallace has no prospect of being elected to the post as he leads the minority party in the coalition.

The new first minister will be whoever Labour decide to nominate for the post.

But the 28-day deadline within which the parliament must act means that Labour will have to decide who its new leader in Scotland should be in little more than three weeks.

Labour's own rules lay down that its leader be elected by an electoral college in which one-third of the votes are cast by MPs and MSPs, one third by the trade unions, and one-third by a ballot of ordinary party members.

But in the event of a contest the party may well find it difficult to implement its full procedure within the 28-day period it will have.