The Information Commissioner must investigate the apparent leak of information about the Scottish Labour leader, a rival politician has said.

Willie Rennie, leader of the Scottish Liberal Democrats, called for the probe after a newspaper reported that Kezia Dugdale twice applied to work for an SNP MSP.

The job applications came during the Labour chief's student days but neither was successful. Dugdale went on to graduate from university and took a job as a Labour researcher before being elected to Holyrood in 2011 and party leader in 2015.

The revelation that she had sought work experience with the Nationalists was made in the Scottish Sun on Wednesday.

Rennie's letter to the Commissioner states: "Reports in the media today have focused on an application from the Scottish Labour leader Kezia Dugdale for employment with the Scottish National Party over ten years ago as she was finishing university.

"Speculative applications for employment are often made with data frequently kept on file by employers for some time afterwards.

"But that application should have remained confidential and I believe that if it was released by the SNP to a journalist it amounts to a serious breach of data protection.

"Scots deserves to know that employers collect, use and keep personal information appropriately and I would invite you to investigate this matter as I am deeply concerned about the implications for civil liberties in this country."

First Minister Nicola Sturgeon spoke on the issue to Heart Radio earlier on Wednesday before the letter was sent.

Sturgeon said :"I think I take from the story today that maybe Kezia Dugdale's political judgement was better when she was 21 than it is today. I don't think it is a big deal.

"None of us really should be, generally speaking, judged all that harshly on the decisions we make as 21 year olds. My message to young people is: get involved in politics if you are interested there has never been a better time to be involved in Scottish politics. I think it is probably more amusing than anything else."

Scottish Labour said an earlier version of the story named Richard Lochhead as the SNP MSP whom Dugdale approached for the jobs. Lochhead's name currently does not appear in the online article.

Shadow Scottish secretary Ian Murray called on Nicola Sturgeon to "condemn" the alleged leak.

Ian Murray said: "The story itself was laughable but data protection is no laughing matter. People need to know that their correspondence with an MSP will be kept private, not leaked to a national newspaper for petty party politics.

"Richard Lochhead is a cabinet minister, he was named in this story by The Sun and neither he or the SNP can avoid questions on this.

"Nicola Sturgeon must break her silence on this issue and condemn this leak of correspondence to one of her cabinet ministers and promise an end to dirty tricks in this election."

However the SNP made clear that "no documents" had been passed to "any outside organisation".

A party spokesperson said: "Why the Lib Dems are being so po-faced about a light-hearted story which has already been laughed off by Kezia Dugdale is anyone's guess.

"It's clear they've resorted to diversionary tactics since they can't win votes on their deeply flawed policies.

"The fact Ms Dugdale asked for a position in the SNP has been very common knowledge in Holyrood circles for a long time. No documents of any kind have ever been given to any outside organisation."

The Information Commissioner's Office states that it will act if it finds any wrongdoing.

A spokesperson said: "We're aware of this story. The law requires organisations to keep personal information secure, and to not keep it longer than is necessary. We'll act where we see clear evidence that this hasn't happened."