A by-election is to be held in Scotland on 24 July, forcing Gordon Brown to order a rushed campaign in a bid to out-manoeuvre opposition parties.

Glasgow East MP David Marshall this afternoon confirmed he was resigning from the Commons by putting in a formal letter to the authorities.

The MP has said he was retiring on doctor's orders, though critics said he was suffering stress over revelations he paid a relative as an assistant from public funds.

A defeat in the Scottish stronghold  -  which Labour holds with a majority of 13,507  -  would be disastrous for Mr Brown, who has already suffered election setbacks in London, the North and the Home Countries. 

Gordon Brown with Health Secretary Alan Johnson: Johnson tried to repair the damage caused by his comment comparing the Prime Minister with a tennis player reluctant to play on Centre Court

Mr Marshall's announcement came as the Prime Minister faced multiple attacks in the form of Labour rebellions, biting criticism from wealthy donors and new signs of union unrest.

Labour MPs fear another dramatic byelection failure just weeks after losing safe Crewe & Nantwich and trailing fifth in Henley behind the BNP.

The poll date is in the middle of Glasgow Fair, the city's traditional summer holiday. Many Glaswegians will be away and turnout could be hit hard.

Health Secretary Alan Johnson attempted to rally supporters  -  and to heal the impression left by his unguarded comparison of the Prime Minister with a tennis player reluctant to play on the Centre Court.

'I think he is a Centre Court performer but the point I was making is that he is not a show-off,' said the embarrassed minister. He will win his matches without being concerned if he is in the limelight."

David Marshall's leaflet for the general election in 2005

Mr Johnson admitted the Government had faced a "maelstrom" of problems but said the Prime Minister was the best leader to bring Britain out of the economic slowdown.

As MPs gathered at Westminster for the first time since last week's humiliation in Henley, backbenchers were urging several key changes in policy.

With the finance Bill entering its last Commons stages, nervous Labour MPs want  public signal that the Government will make concessions over plans to hit family cars with higher excise duty. Rebels also want more generous compensation for those who lost out from the 10p tax band being scrapped.

Meanwhile, the unions put in demands for more workplace rights and higher spending in return for bailing out the party finances.

Mr Brown was mauled by former Labour donors over the weekend who criticised his leadership and threatened to withhold gifts, putting the party deeper in debt to the unions.

It was also reported that former Cabinet minister Peter Hain has been interviewed by police investigating the failure by his deputy leadership campaign team to declare donations from businessmen adding up to £103,000. Mr Hain did not comment on the Times report.

Gordon Brown's attempts to revive his fortunes with a landmark overhaul of the National Health Service was overshadowed by new Labour disarray.