Conservative MSP Alexander Burnett is facing a third probe into his conduct as an MSP, STV News has learned.

Burnett was reported to the standards commissioner by SNP Aberdeenshire councillor David Aitchison earlier this month after failing to declare personal financial interests when asking questions about business rates at Holyrood.

It is the third complaint about Burnett's parliamentary conduct since he was elected to Holyrood in May last year.

Police Scotland are separately conducting an investigation into allegations he failed to properly declare spending on his election campaign last year.

In a letter outlining his version of events to the commissioner, Burnett accuses the SNP of conducting an "attempt to impede my abilities to represent my constituents and waste public time and money".

The Aberdeenshire West MSP asked three written questions to the finance secretary about business rates without declaring his own financial interests in the matter.

According to the Scottish Assessors Association, Burnett is facing a £11,251 rise in his rates bill for two of his firms.

In the letter to the commissioner, Burnett admits the option to declare a registered interest "was not selected when it should have been".

He said: "As you will see, following discussions with one of the businesses, questions were finalised and I approved these to be submitted by my new constituency caseworker on my behalf.

"These questions were submitted for the benefit of my constituents, however, a genuine staff error meant that the tick box 'I have a registered interest' was not selected when it should have been.

"I of course take full responsibility for my new member of staff and she has now had training from the Chamber Desk.

"Unfortunately, this training being in Edinburgh and her being based in Banchory was only possible on February 10, a week after she submitted these particular questions. I apologise for this error."

A senior SNP source said: "It would be bad enough if this was the first time Mr Burnett had run into bother for appearing to flout the rules but he's established an embarrassing track record in failing to meet the high standards that people expect of their MSPs.

"Ruth Davidson will be rightly concerned that one of her newest faces at Holyrood already has a tally of three standards investigations and a police enquiry looming over him just 10 months into the job.

"Once again Holyrood's least self-aware Tory toff has shown he's out for himself and not for his constituents.

"It's absolutely right that any potential standards breach is fully investigated and action taken where necessary."

A spokesman for the Conservatives described the issue as a "simple staffing issue" which has been "addressed".