The First Minister has said she would welcome the publication of all Law Society documents relating to alleged irregularities with property deals carried out on behalf of MP Michelle Thomson.

The transactions led to a solicitor being struck off by the organisation, which referred the case to the Crown Office. A police investigation is now being carried out.

Ms Thomson has denied any wrongdoing but has withdrawn from the SNP party whip.

It has emerged the Law Society raised concerns about the case during meetings with prosecutors in December 2014 and April 2015, but did not formally submit evidence to the Crown until July 2015, after Ms Thomson's election.

Labour leader Kezia Dugdale said there could be a perception "the Scottish establishment is closing ranks to protect one of its own".

During First Minister's Questions at Holyrood, she urged Nicola Sturgeon to back calls for an "independent external inquiry into why it took the Law Society so long to pass on information to the Crown Office".

"We were grateful to the Lord Advocate for him coming to the chamber on Tuesday to make it clear that the delay in pursuing the case against the lawyer representing Michelle Thomson was down to the Law Society," she said.

"So, we know it was not the Crown Office who delayed investigations by over a year, but we don't know who did or why."

She added: "People have to have confidence that system treats everyone the same regardless of party or position.

"The public will not accept any perception, fair or otherwise, that the Scottish establishment is closing ranks to protect one of its own.

"Will the First Minister join me in calling on the Law Society to hold a proper independent external inquiry into this matter and to publish all papers relating to the delay?"

Ms Sturgeon said: "The Law Society of Scotland is an independent regulatory body, and therefore if Kezia Dugdale has questions for the Law Society then I suggest she would be better advised to direct those questions to the Law Society."

She continued: "I think the Law Society should answer all and any questions that are directed to it.

"I cannot answer on behalf of an independent organisation, but I would certainly welcome publication of any or all documents relating to this case."

Ms Dugdale welcomed the First Minister's response but went on to question the SNP's judgement in selecting Ms Thomson as a candidate and its business spokeswoman at Westminster.

She said it would be wrong for her to return as an SNP MP regardless of the outcome of any police investigations.

Ms Sturgeon has said her party was not aware of the Ms Thomson's business dealings until details emerged in newspapers.

Ms Dugdale said: "We still haven't had an explanation for the fact that the First Minister personally appointed Michelle Thomson to lead on business policy for the SNP.

"There is a contradiction here. On the one hand everybody in the SNP praised Michelle Thomson for her business experience, but on the other hand the First Minister says nobody in the SNP knew anything about Michelle Thomson's business experience.

"It doesn't stack up."

She told the chamber Ms Thomson's company had "boasted" that the number of people struggling with their mortgage during the recession was "a great opportunity", and that those who were "emotionally distant could make a huge profit".

"I ask the First Minister, is preying on desperate people ever an ethical way to run a business?"

Ms Sturgeon replied: "No, I don't think it is.

"If those allegations or any other allegations are proven then I, as I said last week, will treat that as a serious matter."

The Labour leader continued: "Isn't it time for the First Minister to admit that Michelle Thomson's business dealing were wrong, that she was wrong to appoint her, and that it would be wrong for Michelle Thomson to return as an SNP MP?"

Ms Sturgeon said she would allow the investigations to take place and act on their conclusions.

"It is because these allegations are serious, and because these allegations are being treated as serious, that right now Michelle Thomson is not a member of the SNP, she does not hold the SNP whip, she is not a spokesperson for the SNP, and she will not be attending the SNP conference," she said.

"That's what happens when serious allegations are raised that concern the SNP."