Pete Wishart and the Good Law Project have joined forces against the Metropolitan Police Service (MPS), lodging a pre-action protocol on Friday.
It comes after the MP for Perth and North Perthshire complained to the MSP Commissioner Cressida Dick over concerns about potential criminality, when an investigation by the Sunday Times and openDemocracy found a number of Tory donors and supporters had been awarded peerages.
The investigation found that 15 of the last 16 Conservative Party treasurers have been offered a seat in the House of Lords, having each donated more than £3 million to the party.
Other Conservative donors have also been ennobled alongside party treasurers. In total, 22 of the party’s main financial backers have been given peerages since 2010 and together have given an estimated £54m to the Tories.
On Friday, the Goodd Law Project and Mr Wishart threatened legal proceesings against the MPS after it said it would not investigate the MP’s concerns.
The service said there was insufficient information to launch a formal inquiry earlier this month, in a letter to the MP.
Mr Wishart said he was concerned the awarding of peerages was a crime, similar to that which was reported to the service in 2006 by his SNP colleague Angus McNeil. At the time four Labour party donors had given around £5m to the party and were subsequently nominated for peerages by former Prime Minister Tony Blair.
The pre-action protocol letter sent on Friday asks the Met share the information and documents they considered before refusing to investigate, any other correspondence or actions taken by the Met in response to Mr Wishart’s referral and the internal record of the refusal.
The Met must begin a criminal investigation over the scandal. If it refuses, it must explain why, or risk judicial review.
Jo Maugham, director of Good Law Project, said: “At the heart of the legal action is a simple ask: that Boris Johnson be subject to the same law as you and me. And if there’s reason to think he has broken it he gets investigated by the police, just like you and I would.”
Mr Wishart added: “The very idea that a place in the House of Lords can be bought for £3 million is something that appalls the people of this country and there is an expectation that this should rightly be investigated.
“Practically all recent treasurers of the Conservative party have been given a place in our legislature, and the only qualification they seem to possess is an ability to gift millions of pounds to Conservative coffers.
“For more than two weeks, Westminster politics has been taken to the gutter with multiple allegations of sleaze and corruption. It is high time that, where there is clear evidence, the authorities properly consider it and investigate.”
The MPS told The Herald it had received the pre-action protocol, with a spokesman saying: “The MPS received a letter before claim on 19th November and will respond to this letter in due course.”