Neil Findlay and Katy Clark welcomed another boost yesterday for their campaigns to become leader and deputy leader of the Scottish Labour party with the backing of another union.

Communications union CWU has become the seventh major affiliate to announce its endorsement of the dream ticket.

CWU general secretary Billy Hayes said he was confident that the leftwingers could lead the Scottish party to victory in next May’s general election and the Scottish Parliament election the following year.

“We know Neil and Katy will be leaders who are committed to defending the rights of working people in Scotland and will work with trade unions to fight for social justice. We are pleased to support them,” he said.

Ms Clark said she was “delighted” by the announcement.

“I spoke out against Royal Mail privatisation at last year’s Labour Party conference and called for the next Labour government to bring it back into public ownership,” she said.

“I am honoured the CWU has chosen to support me as the best candidate to challenge the failed privatisation agenda.

“The Labour Party’s affiliation to ordinary working people is our biggest strength.”

Mr Findlay said that he and the CWU had “a shared agenda of standing up for working people.”

Both Ms Clark and Mr Findlay have already been nominated by the Bakers, Food and Allied Workers Union, public-sector union Unison, general unions Unite and GMB, rail unions Aslef and TSSA and construction union Ucatt.

Unions give supportive nominations in the contest and can recommend candidates to their members, who vote on a one member, one vote basis by postal ballot.

Constituency Labour Party meetings across Scotland will decide this month to which candidates they will give their supportive nominations.

Members of the Holyrood and Westminster Parliaments have substantive nominations.

Candidates required 10 such nominations to get their name on the ballot — but all of the declared candidates managed this without difficulty.

Community, the union for steelworkers and textile workers among other trades, has backed Mr Murphy and Ms Dugdale.

Shopworkers’ union Usdaw has yet to endorse.