The investigation into the SNP’s finances has “moved beyond” the initial reports received, the outgoing chief constable of Police Scotland has said.

Sir Iain Livingstone also defended the time taken for the investigation.

In July 2021 the police confirmed they were investigating complaints made around donations to the SNP. This probe is known as Operation Branchform.

It followed allegations that £600,000 raised for campaigning towards Scottish independence was diverted elsewhere.

In the past several months, three figures in the party have been arrested in connection with this – former leader Nicola Sturgeon, her husband former chief executive Peter Murrell and MSP Colin Beattie, who stood down as treasurer.

All were released without charge pending further inquiries. When she returned to Holyrood in June, Ms Sturgeon said she was certain she had done nothing wrong.

Sir Iain is stepping down as Scotland’s top police officer this August after six years in the job. He will be replaced by Jo Farrell, currently in charge of Durham Constabulary.

Speaking to Radio 4’s Today programme, Sir Iain was asked to address questions over the length of the two-year-long investigation.

He said: “Investigations into the finances of an organisation, the finances of individuals, are often complex.

“Investigations around fraud or investigations around potential embezzlement or investigations around the misuse of funds take time.”

Judicial warrants are needed to obtain financial records, he said.

Sir Iain said: “The time that’s been taken, in my judgment, is absolutely necessary. There’s been a prudent, thorough and proportionate investigation carried out.”

A dedicated team of specialists are involved, he said, who are working closely with prosecutors.

Sir Iain said that if the investigation had not taken place, he would have faced questions of dereliction of duty.

He was asked if the investigation had become “bigger” than the original inquiries.

He said: “It’s moved beyond what some of the initial reports were. That’s not uncommon in investigations such as this.”

Sir Iain said he would not put an “absolute timeframe” on the length of the investigation but that it would be “proportionate and timeous”.

The SNP has consistently said it will co-operate with the investigation.

A review of the party’s governance and transparency was ordered after Humza Yousaf became leader.

Responding to the chief constable’s comments, Scottish Conservative chairman Craig Hoy said: “Confirmation that the investigation into the SNP’s finances has moved beyond the initial complaint only highlights the seriousness of this investigation.”

Scottish Labour deputy leader Jackie Baillie said: “It is right that Police Scotland is investigating every aspect of this case. From what was a single complaint, it now appears that there are multiple lines of inquiry and a can of worms has opened up.

“It is clear that Chief Constable Livingstone and his officers are working hard to shine light on this unedifying period in Scottish politics.”