LONDON (AFP) - The leader of Britain's centre-left Labour party in Scotland said Saturday he plans to step down after a humiliating defeat to nationalists in this month's general election.

Jim Murphy, who lost his own seat on the outskirts of Glasgow in the rout by the pro-independence Scottish National Party (SNP), will leave in June after just five months in the job.

The SNP won 56 out of 59 seats in Scotland in the May 7 vote, while Labour slumped from having 41 seats to just one in what was once one of its strongholds.

His decision to leave comes as Labour nationally also searches for a new leader after Ed Miliband quit following a surprisingly big defeat by Prime Minister David Cameron's centre-right Conservatives.

Murphy said he would introduce a report outlining "a plan for earning back the trust of Scottish voters" before stepping down.

"I'm clear that the answer for the Scottish Labour party will not be found in tinkering with our constitution - we need to think far more deeply than that," he said after a meeting of the party's national executive in Glasgow.

"No option will be off the table except the status quo."

Elsewhere on Saturday, the candidates to replace Miliband as national leader were outlining their claims to the job to activists in London.

Andy Burnham, Yvette Cooper, Mary Creagh and Liz Kendall are the four to declare so far, while frontrunner Chuka Umunna pulled out of the race this week.

Umunna, the party's slick business spokesman, cited "very real concerns" about the impact of press interest in him on "those close to me".