The police investigation into the SNP’s finances has been broadened to consider allegations of “misuse of funds” and “potential embezzlement”.

Police Scotland is investigating whether £660,000 raised by the SNP to fight a second independence referendum was spent on other things.

Nicola Sturgeon, the former first minister, Peter Murrell, her husband and the former SNP chief executive, and Colin Beattie, the party’s former treasurer, were arrested, questioned and released without charge in relation to the inquiry. However, Daily Business has learned of growing concern within the party that charges may follow.

Sir Iain Livingstone, the departing chief constable, confirmed in a radio interview that Operation Branchform has been expanded beyond allegations of fraud.

“It’s moved beyond what some of the initial reports were,” he said, adding that the investigation was taking time because of the complex nature of such inquiries.

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

“You need to go and obtain information from banks and other financial institutions. We can’t just do that automatically.”

Asked whether it was proportionate to put a police tent on Ms Sturgeon’s front lawn, he said: “It absolutely was given the circumstances of that search.”

He added: “The tent was there, as well as all the other measures, to protect the interests of justice and to protect the individuals involved. So it was a proportionate and necessary step.”