Scottish Labour leadership candidate Jim Murphy has stood down from his international development post in Ed Miliband's shadow cabinet.

Mr Murphy said the challenges of reforming Scottish Labour and battling to lead the party and potentially Scotland has made it difficult for him to continue in Mr Miliband's top team.

The race to lead Scottish Labour intensified yesterday with Mr Murphy's rival Neil Findlay securing the support of Unison, Scotland's largest union, and transport Union Aslef, while Unite poured scorn on Mr Murphy's campaign launch in Edinburgh saying his policies to date lack substance.

Mr Murphy conceded he has work to do to get on Unite boss Len McCluskey's good side on BBC 5 Live's Pienaar's Politics today.

Explaining his decision to resign from the shadow cabinet, Mr Murphy told John Pienaar: "I want to dedicate myself full-time to changing Scotland and changing the Scottish Labour Party. It's difficult to do that and to serve in the shadow cabinet and therefore after talking to Ed Miliband over the past couple of days I've decided to stand down from the shadow cabinet"

Asked how he would get on Len McCluskey's good side in order to attract support from the unions, he said: "There are things that I can do and things that I can't. Trying to pick the Scottish Labour Party up, rebuilding a sense of confidence and a sense of belief is doable. Getting on Len McCluskey's good side - that's a job for another day."

Mr Murphy has pledged to reveal his tax plans as his leadership campaign unfolds, but has yet to reveal whether he shares rival Neil Findlay's sympathy for full devolution of income tax.

Mr Murphy dismissed Gordon Brown's warning that full income tax, which is currently supported by all of the parties involved in the Smith Commission on Scottish devolution except Labour, is a "Tory trap" designed to strip Scottish MP of their voting rights yesterday.

But he told John Pienaar that Scotland should retain aspects of the UK tax system.

"One of the important things about a tax system - and we saw this in the financial crisis and crash of 2008 - is how across the United Kingdom and the four nations you have a tax system that supports one another, that spreads wealth around the United Kingdom and those are the sort of tests I want to have," he said.

"Now when Scotland has voted so strongly - with over two million people voting no to stay a part of the United Kingdom - it wouldn't make sense to give up voluntarily one of the real strengths of the United Kingdom, which is: devolved tax system, yes - but while retaining aspects of a UK system and I do think that's important. That's sharing and pooling and that's solidarity that comes from being part of something bigger."