ANAS Sarwar has warned against dirty tricks clouding the Scottish Labour leadership race, demanding respect for the “spirit of the rules” amid claims of a union stitch-up for his rival.

The centrist Glasgow MSP spoke up after reports that Unite had helped left-winger Richard Leonard by signing up almost 3,000 members to its political levy in a single weekend.

The payment makes them eligible to vote in the contest for Kezia Dugdale’s successor.

Sources close to Mr Sarwar said Scottish Labour members “wouldn’t take kindly” to an attempt by Unite to turn the largely autonomous party into Jeremy Corbyn’s “branch office”.

Mr Leonard said it was wrong to “call foul” on the practice.

At a hustings at the UK Labour conference in Brighton, Mr Sarwar said he wanted more people to join Labour or sign up as supporters in order to vote in the contest.

But he added: "We have all got to make sure we play by the rules - that's in terms of the written rules and also the spirit of the rules as well.

"As long as all of us do that, I have no problem with more Unite members or any other trade union members joining this process, voting in this contest and hopefully then engaging with us as well as we return a UK Labour government and also a Scottish Labour government."

Mr Sarwar also pointedly told the hustings he would not be afraid to clash with Mr Corbyn if it was in the interests of Scotland.

He said: "It's about saying, in a grown-up environment, with an autonomous Scottish Labour Party not being a branch office ... that we can take different decisions in Scotland that are right for Scotland's interests."

Mr Leonard responded: "The trade unions are going through due process of deciding who it is they are going to back, and I don't think it's right to call foul about those rules after decisions have been taken.

"If there's a problem with the rules you should say that there is a problem with the rules up front."

He said Unite's support came after a union hustings and it was "not a decision taken by Len McCluskey", the union chief who is close to Mr Corbyn, but "rank and file" Scottish members.