SCOTLAND’S top police officer has defended the use of a blue forensics tent outside Nicola Sturgeon’s home as he suggested that the investigation into SNP finances had "moved beyond" the initial complaint.

Iain Livingstone, who will step down as chief constable of Police Scotland in August, suggested in an interview on BBC Radio 4 that officers were probing potential “embezzlement” or “misuse of funds” in their SNP investigation.

Named Operation Branchform, the probe into SNP finances is looking at how some £600,000 in funds raised to fight a second independence referendum were used.

READ MORE: Police Scotland boss warns of 'ill-informed speculation' over SNP finances probe

Amid the police probe on April 5, former SNP chief executive Peter Murrell was arrested, questioned and released without charge as officers searched both his home address and SNP headquarters.

A blue forensics tent was set up outside Murrell’s home, which he shares with his wife former SNP leader Nicola Sturgeon, in a move that would be questioned as unusual and “over the top”.

The National: The search of Peter Murrell and Nicola Sturgeon’s home continued on Thursday (Andrew Milligan/PA)

But Livingstone defended the use of the tent. “It absolutely was [proportionate] given the circumstances of that search,” he said.

“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.”

The Police Scotland boss also told the BBC that the probe into the SNP had “moved beyond what some of the initial reports were”, adding: “That's not uncommon in investigations such as this.”

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

“Investigations around fraud or investigations around potential embezzlement, or investigations around the misuse of funds, take time. You need to go and obtain information from banks and other financial institutions. We can't just do that automatically.

“We need to go and seek judicial warrants for that. There needs to be a process around that. So the time that's been taken, in my judgment, is absolutely necessary.

“There's been a prudent, thorough, and proportionate investigation carried out.”

Livingstone said that if the investigation had been carried out in any other way then his force would have opened itself up to justified criticism.

He told Radio 4: “What I would say is that had we not carried out this investigation in the manner we have, I would rightly have been accused of a significant dereliction and neglect of duty.

READ MORE: Racism, sexism, and misogyny 'a reality in Police Scotland', top officer admits

“That's not the case. We've done the right thing. The rule of law and the interests of justice must prevail.”

Livingstone has been giving media interviews ahead of his retirement, including one to the Sunday Times in June.

He used that platform to warn against uninformed speculation about the SNP probe.

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

“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.”

Jo Farrell, who is currently in charge of Durham Constabulary, will take over as the head of Police Scotland after Livingstone's retirement