NICOLA Sturgeon has been called upon to break her silence as two further SNP politicians faced controversy over what the Scottish Conservatives described as “yet more allegations of dodgy dealings”.

Backbencher Phil Boswell is being investigated by Westminster’s standards commissioner into the registration of his financial interests.

It follows a complaint by a former Liberal Democrat candidate over Mr Boswell's alleged failure to record that he was a director of a company, Boswell and Johnson Ltd, in the Members’ Register of Interests.

Another of the party's MPs, Dr Lisa Cameron yesterday faced claims of hypocrisy after she campaigned against the sell-off of social housing but built up a property portfolio of former council houses.

A report in the Scottish Daily Mail said the MP for East Kilbride, Strathaven and Lesmahagow owned seven properties, three of which were bought after they were repossessed and after tenants had failed to keep up payments on their mortgage.

Scottish Conservative MSP Alex Johnstone said: “The news that another two SNP MPs are embroiled in yet more allegations of dodgy dealings does nothing for the credibility of the SNP.

“With revelations being published on an almost daily basis, the public will have lost count of how many SNP politicians are in trouble.”

James Kelly, Scottish Labour’s parliamentary business manager, urged the First Minister to speak out on the probe into Mr Boswell’s registration.

He said: “It is right that the standards commissioner has chosen to investigate this case. At the very least Phil Boswell is guilty of the worst kind of hypocrisy; grandstanding against tax avoidance in Westminster whilst using schemes to avoid tax himself.”

Mr Kelly called on the First Minister to “break her silence on Mr Boswell and order an urgent investigation from her party”.

On Mr Boswell, an SNP spokeswoman said he had sought advice from the Register, adding that "as the rules set out by the commissioner for standards makes clear, their inquiry does not imply that there has been a breach of the rules of the House."

She added that Dr Cameron had declared her interests in line with the rules. The spokeswoman said: "The properties were not purchased from the local authority and include, for instance, a flat which Dr Cameron inherited from her late grandmother."

Mr Boswell, a former contract manager in the energy sector, has admitted benefiting from a tax avoidance scheme in the past despite campaigning against them in the Commons.

The MP for Coatbridge, Chryston and Bellshill, said payment was "common practice" in the industry and the SNP has since confirmed the MP has been in touch with HM Revenue and Customs to discuss his tax position.

An SNP spokeswoman said: "Phil Boswell sought advice from the Register of Interests and as the rules set out by the commissioner for standards makes clear, their inquiry does not imply that there has been a breach of the rules of the House."

In September, Michelle Thomson, the MP for Edinburgh West, resigned the SNP whip after she became the subject of a police investigation into alleged irregularities involving property deals.

Two months later, Natalie McGarry, the MP for Glasgow East, also resigned the whip after the police were called in to investigate the finances of Women for Independence, of which she was a founding member.

Both MPs deny any wrongdoing.