JIM Murphy is preparing a campaign to fight for the Scottish Labour leadership and is expected to announce his candidacy later this week, it has emerged, after Gordon Brown ruled himself out of the running for the party crown.

The East Renfrewshire MP and shadow international development secretary has become the clear frontrunner to replace Johann Lamont, whose resignation stunned the party last Friday.

A source said Mr Murphy had not made a final decision, but was making preparations, including assembling a campaign team.

The news came as the former Labour Prime Minister told friends he had no intention of returning to "frontline politics".

Meanwhile, as Labour MSPs and MPs held meetings to discuss the way forward, deputy leader Anas Sarwar faced calls to vacate the role in a move that would allow the party to elect a more balanced team to spearhead a fightback against the SNP.

MPs and MSPs from all sections of the party insisted the party should not be run by two male MPs even for a temporary period.

Their comments piled pressure on Mr Sarwar, Scottish Labour's acting leader, to clear the way for a deputy leadership bid by a sitting MSP.

Possible candidates for the number two role, if it becomes available, include Kezia Dugdale and Jenny Marra, both viewed as rising stars at Holyrood.

But Mr Sarwar's spokesman dismissed calls for a deputy leadership contest as "nonsensical, a complete red herring" and said the Glasgow Central MP had no intention of stepping aside.

However, one Scottish MP, not seen as close to Mr Murphy, said: "The criteria that are most important for the new leader are having a high public profile, political skill and the energy to fight two election campaigns in 18 months.

"That is more important than which parliament they sit in provided, if it's an MP, they commit to seeking election at Holyrood. However, if that's what happens I don't think we can do it without the deputy being a current MSP.

"If the potential number two is seen as being a talent for the future, that works quite well."

His comments were echoed by an MSP who said: "Having two MPs at the helm is potentially a problem not just because they are based at Westminster but, if Jim were to be elected, there would be an issue of gender balance."

Another MSP said Mr Sarwar's position was "increasingly key" as MSPs, party members and those affiliated through their trade union looked to the future.

Mr Sarwar yesterday addressed a meeting of Labour MSPs at the party's Glasgow HQ before flying to London to speak to MPs.

In a statement he said his priorities as interim leader were to deliver a strong package of new powers for Holyrood as part of Lord Smith's devolution process, continue to hold the SNP and Tories to account and to prepare the party for next May's General Election.

Mr Murphy, 47, could expect strong support among MPs and MSPs who see him as a "big beast" able to take the fight to the SNP at the next election.

If he wins, it is thought there could be a Holyrood by-election on the day of the General Election to try to secure the frontbencher a place in the Scottish Parliament. Victory for Mr Murphy would also lead to his resignation from the shadow cabinet, which would lead to a mini-reshuffle, opening the way, potentially, for a return to frontline politics for Alistair Darling.

Next May, Labour will face a concerted challenge from the SNP, when losing a slice of the party's 41 Scottish seats could wreck Ed Miliband's hopes of becoming Prime Minister.

Potential challenger Neil Findlay, Labour's health spokesman at Holyrood, said he wanted Mr Brown to stand but refused to rule himself out of the running if the former PM failed to stand. "Let's see what happens," he said.

The left-winger would be confident of winning backing from the unions, which account for a third of the vote in Labour's electoral college, along with parliamentarians and grassroots members. However, some insiders fear a bruising battle between Mr Murphy and Mr Findlay as it would expose tensions between the right and left of the party and between Westminster and Holyrood.

A source close to Mr Brown said: "For the past four years, on every occasion he has been asked, Mr Brown has made clear he is not returning to frontline politics. That position has not changed."

Meanwhile, there is growing anger at Malcolm Chisholm's comments over the weekend that electing an MP as leader would be a "catastrophe".

One MP said the remark was "totally playing into the SNP's hands". At Westminster last night, Mr Sarwar addressed the full Parliamentary Labour Party before the Scots group, where he praised and thanked the work of MPs in helping secure a victory in the referendum, receiving a round of applause. But when he thanked Johann Lamont for her role, there was no round of applause.

In the Commons, David Cameron had a light-hearted dig at the party's problems. Noting how noisy the chamber was during a debate on Europe, he joked: "It's a bit like a meeting of the Scottish Labour Party."