Police Scotland did not name the arrested man but said a 71-year-old suspect was detained on Tuesday.

"The man is in custody and is being questioned by Police Scotland detectives," the force said.

"A report will be sent to the Crown Office and Procurator Fiscal Service."

It added: "As the investigation is ongoing we are unable to comment further."

SNP treasurer arrest 'highly significant' - politics latest

Following Mr Beattie's arrest, an SNP spokesperson said: "We have no comment on a live police investigation."

The development today deepens the scandal that has engulfed the party regarding its finances and threatens to overshadow a major day for new party leader and First Minster Humza Yousaf.

Mr Yousaf - who had hoped to offer a "fresh start" in a speech today in the Scottish Parliament - admitted Mr Beattie's arrest was "not helpful" but insisted he was still "determined" to set out his vision.

Asked if Mr Beattie had been suspended for the party, the SNP leader said: "I've said already that people are innocent until they are proven guilty."

Mr Beattie is the second arrest of a high-profile SNP figure in just a matter of weeks.

Peter Murrell, the SNP's former chief executive and Nicola Sturgeon's husband, was detained by police earlier this month in connection with the investigation into the party's finances.

He was later released without charge pending further investigations after an 11-hour detention.

At the same time that he was in police custody, detectives seized a £100,000 motorhome from outside the home of one of Mr Murrell's elderly relatives.

In another move that has hit the party, it emerged days after Mr Murrell's arrest, its long-standing auditors Johnston Carmichael quit.

There have been questions hanging over Mr Yousaf after he admitted that the party's auditors had in fact quit months before the official announcement and he had not been aware at the time.

Asked whether it was wrong of Ms Sturgeon not to reveal to SNP leadership candidates the lack of auditors, Mr Yousaf said: "Frankly it would have been helpful to know beforehand.

"I think people have a reasonable question to ask the party around transparency. I have committed to a review of governance with external input."

Explainer - Why have senior SNP executives been arrested and what are police investigating?

Mr Yousaf also said he was unaware the SNP owned the motorhome until he became party leader in recent weeks.

The new SNP leader - who billed himself as the "continuity candidate" during the race to replace Ms Sturgeon - is under pressure to distance himself from his predecessor following the series of damaging events which have overshadowed his first few weeks in the top job.

Over the weekend, a video emerged in which Ms Sturgeon appeared to tell the party's ruling body back in March 2021 to "be very careful" about suggesting the SNP was suffering from financial problems.

There were reports that Mr Beattie had issued a stark message about the SNP's cash flow, warning that it was difficult to balance the books.

Mr Yousaf has faced calls to suspend Ms Sturgeon from the party if she failed to resign herself.

He will address the Scottish Parliament today for the first time since the Easter recess, in a session that reports suggest Ms Sturgeon will be absent for.

On Monday, the party's former leader in Westminster, Ian Blackford, sought to defend Ms Sturgeon and dismissed rumours that she could quit the party.

The Daily Telegraph quoted a source within the party saying she planned to step down "sooner rather than later" amid the ongoing controversies - but Mr Blackford rejected this as "idle speculation", telling the BBC she still had "an awful lot to give".