Claims made by anti-Corbyn MP Ian Murray that the Scottish Labour leadership election is being "rigged" have been dismissed as "baseless smears" by Unite.

The union called on the Edinburgh South MP to withdraw comments made in a letter to the party's general secretary Brian Roy.

In the letter the MP, who is backing Glasgow MSP Anas Sarwar for the top job, warned the leadership election was in danger of being "rigged" in favour of left-wing rival Richard Leonard.

In response, Unite said it was concerned about "repeated and underhand efforts to bring this election and our union into disrepute."

In the letter, printed in full by The Herald, Murray said: "I take absolutely no pleasure at all in writing to you in these terms but I do think 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."

He said he had become "increasingly concerned" at the process that allows people who have signed up as a Labour Party supporter through an affiliated organisation or union to vote.

He criticised Unite, which has thrown its support behind Mr Leonard, for a text message reportedly sent to its members.

Murray said: "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.

"It is important for all of us, whoever is successful, to be assured that the process is robust, fair and credible.

"As a member of the SEC and defender of the rules of the party, I think there are serious questions to answer about the sign-up process that Unite has deployed.

"The text clearly failed to ask the recipients if they supported the aims and values of the Labour Party, nor did it ask them to consent for their data to be shared with the party.

"In order for this process to be fair and robust, the party must reconsider whether any sign-ups from this process are valid."

Murray also questioned the "impartiality" of Alex Rowley after the interim leader was caught on tape backing Mr Leonard, and suggested he should no longer chair a panel set up to vet new members.

A Unite spokesman said: "Ian Murray has been told by the SLP that our members' affiliations are entirely legitimate. We therefore call upon him to withdraw his baseless smears now.

"Unite will be writing to the Labour party general secretary to express our concerns at these repeated and underhand efforts to bring this election and our union into disrepute."

A Scottish Labour spokesman said: "Any affiliated or registered supporter would be expected to support the aims and values of the Labour Party. These sign ups are eligible and within the rules of the leadership contest."