Officers investigating the SNP’s finances are searching for burner phone-style sim cards as part of the investigation, it has emerged. Luxury pens, designer pots and pans, and even a fridge freezer are also being looked at as part of Operation Branchform.

It follows revelations last week that jewellery formed part of the investigation while a campervan bought by the party seemingly to fight the 2021 Scottish elections has been seized by officers.

It is the latest blow to the SNP, who have had to endure the arrest of former chief executive and husband to Nicola Sturgeon Peter Murrell and treasurer Colin Beattie MSP in the last fortnight.

Officers are looking for information from the sims which are commonly used in untraceable phones. They are usually used to stay anonymous and protect the usage and identity of the person who has it.

A source with knowledge of the investigation told the Sunday Mail: “Something police are looking for is sim cards used in unregistered mobile phones. They want to know the numbers connected with these cards which could also contain numbers called and text messages.

“It’s not uncommon for people to have unregistered mobile sim cards which can be bought from any shop, there’s nothing wrong with having a so-called burner phone, but police want a record of these phones in the SNP.”

A second source told the paper: “There is an extensive list of items the police are interested in which will probably be surprising some people. It is mostly high-value items – expensive pens, pots and pans, jewellery, but also a fridge freezer. This is a very extensive inquiry and clearly absolutely no stone is being left unturned.”

Both Murrell and Beattie – who has since quit as treasurer and been replaced by Stuart McDonald MP – were released without charge pending further inquiries.

Speculation is now mounting that Ms Sturgeon could be next to be questioned as part of the operation, which focuses on over £600,000 of money raised in 2017 that was supposed to be ‘ring-fenced’ for a second Scexit referendum.

Dumbarton Labour MSP Jackie Baillie,  LibDem Alex Cole-Hamilton and Tory Craig Hoy.

Scottish Conservative Party chairman Craig Hoy said: “It is crucial the SNP cooperates fully with the police investigation and gives the public the answers they deserve to questions that remain unanswered. Humza Yousaf must also finally suspend the senior SNP MSPs – including Nicola Sturgeon – who are associated with the investigation.”

Scottish Labour deputy leader Jackie Baillie said: “These details raise deeply worrying questions about practices at the heart of the SNP. This arrogant and sleaze-ridden party needs to start operating with some much-needed transparency and consistency – the people of Scotland deserve nothing less.”

Scottish Liberal Democrat leader Alex Cole-Hamilton said: “It looks like Humza Yousaf and his new treasurer have got a hell of a mess to get to the bottom of. I wish SNP politicians were focused on our urgent public service crises like the fact that one in seven Scots are now on an NHS waiting list.”

The Nats are also facing a race against time to employ new auditors ahead of a July 7 deadline after Johnson and Carmichael quit last year. We told on Saturday that senior sources are not confident new ones will be installed.

Both Police Scotland and the SNP declined to comment on the Sunday Mail story.