The general secretary of the country's biggest trade union has launched a strong attack on one of the candidates in the Scottish Labour leadership contest.

Len McCluskey, leader of Unite, said Labour faced the loss of dozens of seats in Scotland, which would make it "hideously difficult" to elect a majority UK government.

Writing on the LabourList blog, Mr McCluskey said he was "delighted" that his union was backing MSP Neil Findlay for the post, adding that his commitment to social justice and a progressive agenda was essential to reconnect Labour with its natural supporters.

He said it was "essential" that MP Jim Murphy did not win, describing him as the candidate "of the past and of division."

He wrote: "He is an advocate - and, let me acknowledge, a powerful and committed advocate - for the policies which have led Scottish Labour to its present pass. His victory would be all the SNP's Christmases come at once.

"He supports austerity and 'economic credibility' with the City of London. He was a strong backer of the disastrous Iraq war, and made it clear he would have liked to see military action against Syria last year. He backs extending privatisation in the public services. He is a pioneer of tuition fees for students.

"At a time when Scottish Labour desperately needs to reconnect with its social democratic roots, he is the candidate of a reheated Blairism which in my view will be a sentence of political death for many Scottish Labour MPs, and for the prospect of a Labour victory next May."

Mr McCluskey said there was no future in a politics which aimed to put Labour to the right of the SNP.