Nicola Sturgeon refuses to answer questions related to live police investigation

       The crisis for the SNP has escalated even further, as Scotland's chief constable has confirmed that the police investigation into the party's finances has been expanded.

       The scope of the investigation will now include allegations of "misuse of funds" and "potential embezzlement", Sir Iain Livingstone confirmed.

       Operation Branchform was initially a fraud investigation.

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

       Speaking to BBC Radio 4's Today programme, Sir Iain said: "It’s moved beyond what some of the initial reports were."

       Nicola Sturgeon was arrested and released without charge earlier this year (Image: Getty)

       When asked why the investigation has taken more than two years, Sir Iain explained: "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."

       A tent was erected in the garden of Nicola Sturgeon and Peter Murrell's home (Image: Getty)

       He added: "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."

       When asked whether he felt it was proportionate to put a police tent on former SNP leader Nicola Sturgeon's front lawn, Sir Iain told the BBC it was "proportionate and necessary".

       He said: "It absolutely was given the circumstances of that search."

       "The tent was there, as well as all the other measures, to protect the interests of justice and to protect the individuals involved.

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       "So it was a proportionate and necessary step."

       Ms Sturgeon and her husband Peter Murrell, the former SNP chief executive, have both been arrested and released without charge int he investigation.

       The party's former Treasurer Colin Beattie has also been arrested and released without charge.

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