The SNP has called for the Metropolitan Police to launch an investigation into a Tory "cash for honours scandal". 

It comes after an investigation by The Sunday Times and Open Democracy found 15 of the last 16 of the Conservative Party's treasurers have been offered a seat in the Lords having each donated more than £3 million to the party.

It found 22 of the party's main financial donors have been given peerages since 2010. They donated a combined total of £54 million. 

A former Tory minister described it as a “scandal in plain sight”, while a former party chairman told the paper: "The truth is the entire political establishment knows this happens and they do nothing about it ... 

"The most telling line is once you pay your £3 million, you get your peerage."

The most controversial appointment was that of Lord Cruddas, who took his seat after Boris Johnson rejected the advice of the House of Lords Appointment Commission not to grant him a peerage.

The Tories have denied any link between the donations and the nominations to sit in the Lords, with Environment Secretary George Eustice claiming their expertise made them "valuable" members of the Upper Chamber.

He said: "They are philanthropists who give huge amounts to charity, who have been very successful in business and, therefore, on those grounds ought to be considered for the Lords."

SNP MP Pete Wishart said: "The Tory corruption scandal is growing worse by the day. 

"It's now beyond all doubt that the honours system has been abused by the Tories. 

"The Metropolitan Police should launch a fresh cash for honours investigation to determine whether a criminal offence has been committed.

"It is utterly appalling that so many millionaire Tory Party donors have been handed life peerages by Boris Johnson and his predecessors. 

"But this isn't just a scandal for the Tories - the Labour Party and Liberal Democrats have also been dishing out peerages to donors as though they were sweeties. 

"It is corruption plain and simple - and it absolutely stinks.

"The undemocratic House of Lords is packed with hundreds of Tory, Labour and Liberal Democrat donors and cronies, who are making laws without being elected and claiming allowances at our expense. 

"It should have been abolished centuries ago but, whenever they've had the opportunity, the Tories and Labour Party have instead chosen to continue benefiting from the broken system - milking taxpayers for every penny they can get.

"This is just the latest scandal for Boris Johnson who seems to believe he is immune to abiding by the rules everyone else does. 

"Whether it's cash for peerages, changing the standards system to suit him best, or soliciting dodgy donations for the refurbishment of flats and holidays, he is reigning over a system that he's using to benefit him and his party.

"People in Scotland are looking in horror at what's going on at Westminster. The sooner Scotland can become an independent country, and shake off this broken system, the better."