Two former Labour First Ministers warned Gordon Brown yesterday that he must not try to influence the outcome of the contest to succeed Wendy Alexander as leader of the Scottish Labour Party.

The message to the Prime Minister to “back off” came from Jack McConnell and Henry McLeish, once rivals for the top job in Scottish politics, and showed how Mr Brown's hold over Labour north of the Border is slipping.

Other senior Labour figures said that if Mr Brown attempted to annoint any candidate for the job, it would be “the kiss of death”.

Mr Brown's loss of power in Scotland is dramatic. His backing for Ms Alexander's leadership campaign last year was widely seen as ensuring that she was elected unopposed as potential rivals dared not risk crossing the new Prime Minister.

Yesterday's warning to Mr Brown comes as Labour looks to hold an early by-election in Glasgow East, possibly on July 24. The belief is that a quick contest, after the resignation of David Marshall, the long-serving MP, offers Mr Brown the best chance of avoiding the humiliation of defeat in a Labour heartland seat - an outcome that could trigger a terminal political crisis for the Prime Minister.

The SNP has promised to “throw the kitchen sink” at Glasgow East in an attempt to win it. Senior Labour MPs said that it was vital for the party to hold the seat. “A win, any kind of win, will be enough,” said one colleague of Mr Marshall.

The first shot across Mr Brown's bows yesterday came from Mr McConnell, who said in an interview on the Politics Show on BBC One that the by-election had to be seen to be conducted by the party in Scotland.

Mr McConnell, in a clear reference to Mr Brown and his Westminster-based allies, added: “One of the key factors has to be that members of the Scottish Parliament make a choice without any influence either from me or from senior figures in the party leadership elsewhere.”

Hours later Mr McLeish, who was backed by Mr Brown to become First Minister in 2000, said: “This is an election that is for Scotland, involving MSPs who want to be leader. London should have an interest in what is happening but not become directly linked with the process.

“It would be good if London left the Scottish party to deal with it. This is the right thing to do and sends a clear message that this is a Scottish affair and that Westminster, for the first time in a decade, is stepping back.”

A senior Scots Labour figure backed this view, telling The Times: “In the past leaders in London decided who leads the party in Scotland. This is the chance for the party in Scotland - and no one else - to decide who is the leader in Scotland.

“Certainly, in the light of Brown's present troubles and the people he has foisted on us in the past, it will be the kiss of death for someone if they're seen to be backed by Gordon Brown.”

The leadership contest comes after Ms Alexander's resignation as Scots Labour leader on Saturday after Holyrood's Standards Committee suspended her from Parliament for a day for breaking rules on donations.

Andy Kerr, the front-runner to succeed Ms Alexander, was consulting family and friends yesterday on whether to stand. He would be Mr Brown's least favoured candidate because he is close to Mr McConnell, a long-time opponent of Mr Brown.

Cathy Jamieson, Scottish Labour's deputy leader, hinted strongly yesterday that she was likely to stand.

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