Sir Iain Livingstone has robustly defended the long-running police investigation into SNP finances amid concerns the probe is dragging on.

The former chief constable of Police Scotland spoke out almost a year on from when the inquiry escalated with the search of the home of Nicola Sturgeon and her husband Peter Murrell, and the search on the same day of the party's headquarters in Edinburgh.

Mr Murrell, the SNP's former chief executive, was arrested on the same day as the searches of the two properties. He was later released without charge pending further inquiries.

The search and erection of a blue forensic tent outside Mr Murrell's and Ms Sturgeon's home was later criticised by senior figures in the SNP.

READ MORE: Chief Constable urged to update public on three-year SNP fraud probe

Sir Iain retired last August and is now leading Operation Kenova, a long-running investigation relating to the Troubles in Northern Ireland. 

Operation Kenova delivered its interim report on the activities of a British Army informant code named Stakeknife, who was a member of the IRA's internal security unit, earlier this month.

In an interview with the Herald on Sunday this weekend, Sir Iain reveals why he decided to take on the highly sensitive role, discusses the findings to date and the future of the ongoing investigation.

The Herald: Former Police Scotland chief constable Sir Iain Livingstone.   Photo: Gordon Terris/The Herald

Speaking to The Herald Sir Iain yesterday he was pressed on concerns among senior figures in the SNP that the ongoing investigation was disadvantaging the party in the run up to the election.

He said: "We have always acted in the interests of justice and the rule of law. The political circumstances are around us at all times. I know we have acted with due process.

"But I have been retired a matter of months now and the matter of Branchform is no longer a matter for me."

He was also asked whether a £110,000 campervan at the centre of the investigation should be returned to the party.

The luxury vehicle was towed away by the force in April last year from outside Ms Sturgeon’s mother-in-law’s house in Dunfermline as part of the force's inquiries.

READ MORE: Operation Branchform: Complainer demands action on probe

In a broadcast before the SNP’s national council in Perth on Saturday, STV’s Colin Mackay said that with an election this year, senior figures in the party wanted the campervan back either to use during the campaign, or to sell to help raise funds for it.

Asked if the vehicle should be returned, he said: "I don't think anything should be happening until there is a decision from the Crown Office."

The Herald also pointed to comments he made in July last year when he said "the sooner Operation Branchform is over the better for everyone" and was asked if he still believed that to be case nine months on.

"I said the sooner things come to a head for everyone, the better and I still believe that," he said.

"The police have always worked very very closely with prosecutors, the Crown Office and the fiscal service and I am sure that is continuing."

Sir Iain was pressed on whether his successor as chief constable Jo Farrell should provide an update on the investigation.

"That is not a matter for me to give advice to Jo Farrell," he said.

"I would always be here on a personal, confidential basis, to speak with Jo. She's got many challenges ahead and I want her to do really well, for the force to do well.

"So I wouldn't publicly give Jo Farrell any advice. I think that would be inappropriate."

He again rejected criticisms, made by SNP figures, including its chief executive Murray Foote, that the operation was heavy handed in terms of the search of Ms Sturgeon and Mr Murrell's home and the erection of an evidence tent outside their home.

"I think it was proportionate and necessary, as I said at the time, and I still believe I would have been in neglect of duty had we not acted as we did," he said.

Asked about the revelation that some SNP figures wanted the campervan back, First Minister Humza Yousaf said on Saturday he would not comment on a live police investigation.

However, another senior party official told The Sunday Times: “We want our assets back.”

Stephen Flynn, the party’s leader in Westminster, who is going to Germany with thousands of other Scotland fans for the Euro 2024 football tournament in June, made light of the story at the weekend.

“We could perhaps lend the campervan out to the tartan army, it will save folk having to pay for these extortionate hotels,” he joked.

After the vehicle was seized it was later confirmed by Mr Yousaf that it was owned by the party.

The First Minister admitted he only found out the SNP had purchased the motorhome shortly after he became SNP leader.

The former Scottish Conservative leader Ruth Davidson wrote on X, formerly Twitter at the weekend:

“I hope the SNP absolutely lobby Police Scotland for the campervan back. Vocally and often. Keep all those news programmes flashing up pictures of police tents and seizures.”

Ms Sturgeon and the SNP's former national treasurer Colin Beattie were both later arrested and also released without charge. Ms Sturgeon was arrested in June and Mr Beattie in April last year.

The former first minister has denied any wrongdoing.

Prime Minister Rishi Sunak has said his "working assumption" is that the UK will go to the polls in the second half of the year.

In recent weeks people who have made complaints to the police relating to SNP finances have called for Ms Farell to provide an update on the inquiry.

The probe was launched in July 2021.

In July last year, Sir Iain Livingstone gave an interview in which he provided new information on the progress of Operation Branchform.

He told BBC Radio 4 that it had “moved beyond” the initial complaint to look at “potential embezzlement” and “misuse of funds”.

A Police Scotland spokesperson said last night: "As the investigation remains ongoing we are unable to comment."

It is understood that the Crown Office and Procurator Fiscal Service has not received a Standard Prosecution Report on Operation Branchform. 

A spokesperson for the Crown Office and Procurator Fiscal Service said: “Senior professional prosecutors from COPFS and an Advocate Depute are working with police on this ongoing investigation.

“It is standard practice that any case regarding politicians is dealt with by prosecutors without the involvement of the Law Officers. All Scotland’s prosecutors act independently of political interference.

“As is routine, to protect the integrity of ongoing investigations, we do not comment in detail on their conduct.”

* Read Sir Iain Livingstone's full interview with the Herald on Sunday this weekend.