Scottish Conservative leader Douglas Ross MP is “knee-deep in the Tory sleaze scandal”, the SNP has claimed, after it emerged he failed to declare thousands of pounds of extra earnings.
Mr Ross has referred himself to the Standards Commissioner and said the omission was a "mistake".
According to reports in The Herald, the MP failed to declare outside earnings from his second job as an MSP and third job as a football referee.
The undeclared income includes £6,728.57 from 16 football matches in 2021 and 2020, and £10,745 in a top-up salary from his role as an MSP.
The top up salary paid to an MSP who is also an MP is £21,490 for a whole year.
Mr Ross has only been a list MSP for the Highlands and Islands since May - so he failed to declare six months' worth of earnings.
SNP Westminster deputy leader Kirsten Oswald MP hit out at Mr Ross for "failing to declare thousands of pounds from multiple side hustles" which she said was "a clear breach of the rules".
“It is time to blow the whistle on Tory sleaze.
“People in Scotland deserve better than this and Mr Ross must finally decide whether he wants to be an MP, MSP or full-time referee.
“By desperately clinging on to his Westminster seat, Mr Ross has scored an own goal.
“Voters are not impressed, and people will rightly question whether he’s doing it to make more money or because he’s secretly planning to quit as an MSP when he is inevitably replaced as Scottish Tory leader.”
In a statement to The Herald, Mr Ross said: "This was an error on my behalf that shouldn't have happened, and I apologise for not registering these payments on time," Mr Ross said in a statement to The Herald.
"Since realising my mistake last week, I contacted the Office of the Register of Interests and made them aware of the situation.
"All payments have now been declared, including those from my MSP salary that are donated to charities."
Mr Ross' MSP salary is understood to be paid to charities, with payments having been made to the RNLI in Buckie, Keiran's Legacy, Riding for the Disabled, Moray Women's Aid and Shopmobility Moray.
Later speaking to BBC Radio's Good Morning Scotland, Mr Ross said: "It was a bad error on my behalf.
"I've obviously done it [declared earnings] throughout the time I've been an MP but there was a period at the end of last year - I've tried to work out why - I missed 16 games.
"I don't know why I did that and I noticed the mistake myself last week. I got in touch with the parliamentary authorities. I worked with them to get the register up to date. I am extremely sorry.
"This was a bad error. It was all of my own making and I tried to rectify it as soon as it came to light."
It is understood Mr Ross has been injured since January and has not officiated any professional games since then.Allegations of "sleaze" have dogged the Tory party in recent weeks and on Thursday, the chancellor admitted to ITV News that the government "needs to do better".
Rishi Sunak's comment follows the government's attempt to change standards rules to prevent a Tory MP being suspended, as well as claims another MP breached parliamentary law by using his Commons office for a second job.
Mr Sunak told ITV News it "wouldn't be right to comment" on individual cases but said: "As a government, we need to do better than we did last week and we know that".
Rishi Sunak weighs in on the recent allegations of Tory "sleaze"
Tory MP Owen Paterson was found by the Commons standards watchdog to have repeatedly broken lobbying rules. Last week, a majority of Conservatives voted to reject his suspension and decided the entire system for scrutinising MPs' behaviour needed to be overhauled.
This week, Geoffrey Cox, another Tory MP, refuted claims he broke parliamentary rules by taking a high paying external job and spending part of lockdown working from the British Virgin Islands.
While on Friday it emerged that a Conservative MP who suggested Marcus Rashford should stick to his day job playing football, rather than politics, herself has a second job.