The Parliamentary Commissioner for Standards is investigating South Basildon and East Thurrock MP James McMurdock over allegations he failed to register his business interests.
He was one of five Reform UK MPs before he quit the party this week amid allegations over his eligibility to have claimed £70,000 in bounceback loans during the pandemic.
McMurdock, who is listed by Companies House as a director of Gym Live Health and Fitness Ltd, now sits as an Independent MP for the Essex constituency.
He has been approached for comment.
On Wednesday, Labour MP Jon Pearce asked the commissioner to “investigate whether James McMurdock MP is in breach of the rules of conduct for MPs”.
Pearce wrote to the commissioner, saying “parliamentary rules state this directorship should be listed”.
The company, along with JAM Financial Ltd, where McMurdock was previously a director, has overdue accounts.
McMurdock said via social media that “all my business dealings had always been conducted fully within the law and in compliance with all regulations”.
Last weekend, he asked Reform to temporarily suspend the whip as a “precautionary measure”, and the party said it was carrying out an internal investigation.
On Tuesday, he resigned from the party, saying that after he “had a chance to take specialist legal advice” he had “decided to continue my parliamentary career as an independent MP”.
South Basildon and East Thurrock was the last seat to declare in the 2024 general election following a full recount. McMurdock beat the Labour candidate by 98 votes in a seat that was previously held by the Conservatives.
Under parliamentary rules, MPs should declare any earnings over £100 and any interests that “might reasonably consider the interest to influence their actions or words as an MP”. McMurdock has not declared any directorships.
Mistakes on the register can be corrected by MPs, but serious breaches can lead to formal sanctions, including suspension from Parliament.