POLICE Scotland's outgoing Chief Constable has defended the force's investigation into the SNP's funding and finances, describing it as “proportionate and necessary.”

For two years detectives have been investigating whether £660,000 raised by the party specifically to fight a second independence referendum was spent on other things.

In April, officers spent two days searching the Glasgow home of Nicola Sturgeon and her husband, Peter Murrell, erecting a blue forensic tent on their front lawn.

Supporters of the former first minister described the raid as a "grotesque circus."

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Speaking to the Sunday Times, Chief Constable Sir Iain Livingstone defended his officers.

“Operation Branchform has been a long-going investigation,” he said.

“Police Scotland were asked to look at a number of assertions that were being made – we always do that, it is our duty – then we seek evidence to see if there is any substance in them.

“Then, as matters progress, at an appropriate time we discuss that with independent prosecutors under the Crown Office and Procurator Fiscal Service.”

Sir Iain – who is due to leave the post in August – added: “When we carry out the search we will put processes in place that are proportionate and necessary to the action being carried out and to the inquiry and its terms, and I am satisfied that the steps we have taken are proportionate and necessary.

“Stating opinion or speculation without having the knowledge and information that exists is damaging… because it infringes the rights of individuals.

“Operation Branchform has integrity, it is expected to have rigour. If the operation had not been pursued I would rightly have been accused of neglect of duty.”

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Asked specifically about the tent, the Chief said: “I was aware of it and was supportive of it because I knew the circumstances and the rationale for utilising it, and part of it was to protect rights of individuals.”

Mr Murrell was arrested and questioned for nearly 12 hours, before being released without charge, pending further investigation. 

Two weeks later, the party’s then treasurer Colin Beattie was arrested. He too was eventually released without charge, pending further investigation.

Asked if there would be any further arrests, Sir Iain said: “I would never comment on operational matters."