Scottish Labour leader Jim Murphy has resigned after the party was virtually wiped out by the SNP, saying the party was being damaged by interference from union boss Len McCluskey.

Mr Murphy said he had been forced to announce he would be stepping down after being at the "centre of a campaign" by the London leaders of the Unite union and its general secretary, Mr McCluskey.

He said they had attempted to blame the disastrous General Election result for Labour on the failure of the Scottish Labour Party, in a "grotesque insult" to all those who had campaigned north of the border.

While Mr Murphy won a vote of no confidence in his leadership he said he could no longer remain at the top when this small minority, who had opposed his appointment in the first place, continued to divide the party.

Mr Murphy declared war on interference by Mr McCluskey, saying the Labour leadership of both the UK and Scotland should not be governed by the "grudges and grievances" of one man.

Speaking at a news conference after the confidence vote, Mr Murphy said: "The Labour party's problem is not the link with trade unions or even the relationship with Unite members, far from it. It is the destructive behaviour of one high-profile trade unionist.

"One of the things about standing down is that you can say things in public that so many people in the Labour Party only say in private. So whether it's in Scotland, or the contest to come across the UK we cannot have our leaders selected or deselected by the grudges and grievances of one prominent man.

"The leader of the Scottish Labour Party does not serve the grace of Len McCluskey and the next leader of the UK Labour Party should not be picked by Len McCluskey."

He added: "Len McCluskey and the Unite leadership are the type of people who could pick the wrong winner in a one-horse race."

Mr Murphy said he wanted to ensure the next Scottish Labour leader should be elected using the one member, one vote system, which does not give undue prominence to the views of the unions.

He said he will table his resignation next month with a view to having a successor in place by summer.

Union vote

Ed Miliband's leadership was plagued by the fact that his election was based not on party support, but on union support because of the party's "electoral college system", which gives a third of the vote to the unions.

His brother, David, had won greater support from members and MPs but did not have enough backing from the unions to secure the top job.

However, when leader, Mr Miliband oversaw a change to the system, which means all trade union members must become party members and each party member will get a vote.

Any attempt by Labour leaders to redefine the party's links with the unions is fraught with financial peril because they remain by far and away the biggest donors.

Mr Murphy's comments come after the party's dismal showing at the election was compounded by confusion over the leadership contest to replace Mr Miliband.

Shadow business secretary Chuka Umunna, an early favourite, ruled himself out of the race just days after announcing he was running for the top job.

He said he was not comfortable with the "added level of pressure" a leadership bid entailed. It prompted speculation that journalists had uncovered a story about his past.

Chancellor George Osborne said on Saturday the leadership race had "descended into farce".

Other leadership hopefuls, Andy Burnham, Yvette Cooper, Tristram Hunt, Liz Kendall and Mary Creagh have been making their pitches at a Progress conference.

They said they had not anticipated the scale of Labour's election defeat but that some of them had raised concerns over the direction of the party.

Unite Scottish secretary said: "Jim has done the decent thing. Scottish Labour needs to recover, re-engage and reform. It can now begin that process."