SCOTTISH Labour’s most senior official has condemned a leak of private correspondence in the bitter contest to succeed Kezia Dugdale as an “attempt to undermine the leadership process”.

General Secretary Brian Roy said the unauthorised disclosure of a letter written by Edinburgh South MP Ian Murray, who raised concerns about a sign-up of new members by the Unite trade union, was an “intentional act” to bring the party into “disrepute”.

However, in an apparent dig at Mr Murray, Mr Roy suggested the party's former shadow Scottish secretary had relayed the concerns on behalf of others and requested that colleagues do not act as “intermediaries” in future.

The battle to replace Ms Dugdale, which has pitted centrist candidate Anas Sarwar against left-winger Richard Leonard, has been tainted by feuding.

A large part of the tension centres around the strategies adopted by supporters of both MSPs to sign up new members and supporters ahead of the ballot which opens in the next two weeks.

Mr Leonard’s backers in the Unite trade union are believed to have recruited thousands of “affiliated” supporters, while Mr Sarwar’s circle has embarked on a huge sign-up of members.

As reported last week by The Herald, Mr Murray, who is backing Mr Sarwar, complained to Mr Roy about a Unite text message that led to the mass sign-up.

“There is no doubt whatsoever that the way in which Unite has signed up affiliate members to vote in the leadership election is against the rules of the Scottish Labour Party and the process,” Mr Murray wrote.

He added: “We are in danger of undoing all the progress we have made in the last year because the defence of the leadership election process is, at best, clumsy and, at worst, being rigged for a particular process.”

At the time, a party source dismissed the Murray letter as a “massive diversionary smokescreen” to take attention away from the membership recruitment pursued by Sarwar supporters.

In an email to members of Labour’s governing Scottish Executive Committee (SEC), Mr Roy wrote of his “frustration and anger” at the leak.

The email, which has also been leaked, stated: “A private letter to me from a member of the SEC was leaked to a national newspaper. I believe this to be an attempt to undermine the leadership process, and an intentional act of bringing the Labour Party into disrepute.”

He continued: “I accepted this letter as private correspondence and responded to it after consultation with the Procedures Committee. It was clear to me that this was concerns raised by a member of the SEC, not on behalf of any third party.”

Mr Roy added: “Had it been clear to me that this letter was on behalf of anyone in particular, I would have asked for their details to contact them directly, or for them to contact me. Members of the Scottish Executive Committee have no need to act as intermediaries between me as Procedural Secretary and party members.”

In future, the general secretary said all concerns should be directed to him, and not “undertaken as a cause by individual members of the Executive”.

In his letter, Mr Roy concluded: “This briefing to the press is counter-productive and cannot go on. I would appeal to all of you. Please use whatever influence you have to deter this wilful and intentional damage to our party.”

Mr Roy, who is effectively in charge of the party machine, signed off his angry email with “in comradeship”.

A party source said that Mr Murray contacted Mr Roy after party members raised concerns with the MP, an action the insider said was “reasonable”. Mr Murray declined to comment on Mr Roy’s email.

The ballot opens later this month and the result will be announced on November 18th.

Scottish Labour said it would not comment on leaks. An SNP spokesperson said: "There will be no winners in this embarrassing Scottish Labour leadership contest that’s seen the dirty laundry of both candidates gracelessly aired in public.”