WESTMINSTER’S sleaze watchdog has been called upon to investigate whether former SNP MP Michelle Thomson broke parliamentary rules or brought the House of Commons into disrepute over her property dealings.

A Conservative backbencher has written to Kathryn Hudson, the parliamentary commissioner for standards, urging her to launch a probe to see if the members’ code of conduct has been breached.

Last week, Police Scotland launched an investigation into alleged irregularities with 13 property deals carried out on Ms Thomson’s behalf, which had led to solicitor Christopher Hales being struck off by the Law Society of Scotland for professional misconduct.

In the letter to Ms Hudson, Andrew Bridgen, MP for North West Leicestershire, says: “This case raises serious questions regarding the professional integrity required from a prominent public servant. I, therefore, urge the Office of the Parliamentary Commissioner for Standards to conduct a full investigation into Ms Thomson and the associated property transactions, which have given cause for concern”.

Ms Thomson, the Edinburgh West MP withdrew from the SNP whip; she was the party’s business spokeswoman at Westminster.

She denies any wrongdoing and has made clear she will co-operate fully with the police inquiry.

The standards commissioner is duty-bound to look into any complaint made against an MP to see whether or not it is within her remit and if there is sufficient evidence to justify a full inquiry.

Ms Hudson is currently investigating former Scottish Secretary Alistair Carmichael over so-called Frenchgate, concerning the leak to the Press he authorised of a false account of a conversation between Nicola Sturgeon and the French ambassador, which was an attempt to smear the First Minister during the General Election campaign.

If an investigation is launched, there are three potential outcomes: there is insufficient evidence to show a breach of the code has taken place; there has been a minor breach, which will lead to “rectification”, whereby the MP apologises and makes right the breach, or there has been a serious breach.

The latter will mean the matter is considered by the Commons Standards Committee, which can lead to an MP being suspended for a period of time, having their pay halted during this period or being expelled from parliament.

The code of conduct makes clear MPs have to uphold the law and act at all times with probity and in the public interest. In carrying out their parliamentary and public duties, MPs are expected to observe seven general principles: selflessness; integrity; objectivity; accountability; openness; honesty and leadership.

The rules state: “Members shall never undertake any action which would cause significant damage to the reputation and integrity of the House of Commons as a whole or of its Members generally.”

In his letter, Mr Bridgen, a former officer in the Royal Marines, relates to the commissioner the “serious allegations of professional misconduct” made against Ms Thomson.

Meanwhile answering questions at Holyrood, Scotland’s top law officer said the police investigation into the 13 property deals could be widened.

While Ms Thomson is not under investigation personally, Frank Mulholland, the Lord Advocate, said that police would “follow the evidence”.

He said: “The referral to Police Scotland is in relation to the solicitor, who is subject to the Scottish Solicitors Disciplinary Tribunal findings. Police Scotland have a duty in any criminal investigation to follow the evidence and where that takes them.

“If during a police investigation evidence arises that other persons have been involved in criminality, fraud or whatever crime... then Police Scotland, I have complete faith in them, that they will act and do the right thing."

Mr Mulholland also restated the Crown Office’s position that it had not known about the identity of Mr Hales’s clients until it was formally passed a report by the Law Society in July this year. It instructed police to begin an investigation six days later.

The case had been raised informally by the Law Society at two previous meetings, although the identity of Mr Hales’s clients was not disclosed.

Following the exchange at Holyrood, Labour called for an immediate inquiry into communication between the Crown Office and the Law Society.

Jackie Baillie, the party’s public services spokeswoman, said: “It took a year after the lawyer was struck off for the Law Society to properly inform the Crown Office but just six days for the Crown Office to order a Police Scotland investigation. Something doesn’t add up.

"The pressure is now on the Law Society to come clean about who knew what and when. We need full transparency about why it took so long for the Law Society to pass on information about this case. Without full transparency it will look like the Establishment is closing ranks to protect one of its own.”

Michelle Thomson’s solicitor Aamer Anwar said: “We have advised Ms Thomson that it would be inappropriate to comment on such matters and you will appreciate that she has already volunteered to assist Police Scotland with their investigation, despite no requirement to do so. Michelle Thomson maintains that she has always acted within the law.”