The SNP has made a formal complaint to the Metropolitan Police over claims the Tories awarded peerages to donors who gave millions to the party.
SNP Commons Leader Pete Wishart asked Scotland Yard to investigate whether the "cash for peerages" allegations were in breach of the law.
Boris Johnson's party has been accused of abusing the honours system by giving seats in the Lords to a select group of donors who each donated large sums to the party.
An investigation found that eight of the nine last Tory main treasurers had been offered peerages - with each of those appointed since 2014 donating at least £3m.
In his letter to the Met, Mr Wishart wrote that the allegations were "deeply undermining public trust and confidence" and should be urgently investigated.
He suggested the police should focus on whether Boris Johnson, his immediate predecessors as PM and Tory officials had breached the Honours (Prevention of Abuses) Act 1925.
It is the latest sleaze allegation levelled at Mr Johnson's Government in the wake of the Owen Paterson scandal which saw his personal ratings slump to their lowest ever level.
The SNP was behind the original complaints to the Met Police in the cash for peerages scandal that rocked Tony Blair's government in 2006.
Scotland Yard has been approached for comment but the Mirror understands that Met chief Dame Cressida Dick has assured a speedy response to the letter.
Mr Wishart told the Commons it was "cash for honours 2.0", telling MPs the "price to get into the House of Lords has gone up from £1 million from New Labour to £3 million from the Conservatives".
He added: "It now seems that nearly all the past treasures of the Conservative Party of later years are in that place, wearing their ermine, taking a part in the legislative decisions of this country.
"The only characteristic they seem to have, the only defining feature that seems to get them a place in that House, is the fact they're able to give several million pounds to this Government."
A government spokesman said: “Peerages reflect long-standing contributions to civic life and also a willingness to further contribute to public life as a legislator in the second chamber.
“It is wrong to criticise individuals being honoured just because they have also chosen to support or donate to a political party.
"Donations should be transparent, but that is not an excuse to knock people for broader philanthropy, enterprise and public service."
