Labour MP Jess Phillips under investigation for breach of parliamentary rules

The allegation relates to paragraph 14 of the code, which concerns the registration of financial interests.

Under the code, MPs must be “open and frank in drawing attention to any relevant interest in any proceeding of the House or its Committees, and in any communications with Ministers, Members, public officials or public office holders”.

Daniel Greenberg, the commissioner, confirmed the probe, adding that it was in relation to the “registration of interests under category one of the guide to the rules – employment and earnings”.

Phillips was reprimanded last year after an investigation by the watchdog found she had failed to register a number of outside earnings within the 28-day deadline set by the Commons.

This included a payment for a guest appearance on the TV show Have I Got News For You, which the shadow safeguarding minister said there had been an “administrative oversight”.

At the time, the then commissioner Kathryn Stone said "there was no deliberate attempt to mislead".

Stone said: "This has been a finely balanced decision.

"Given the number and total value of the registrations involved, I gave serious consideration to referring the matter to the Committee on Standards for sanction.

"I found that, based on the information available to me, the breaches were inadvertent, insofar as they were the result of a longstanding inattention to administrative detail on the part of Ms Phillips and that there was no deliberate attempt to mislead."

Phillips is the ninth person currently under investigation by the commissioner.

A Labour spokesperson said: “It would be inappropriate to comment on an ongoing investigation."

Among those includes Prime Minister Rishi Sunak who is being investigated over whether he broke rules by failing to declare an interest in a Budget measure which may benefit his wife through her shares in a childcare firm.

Former health secretary Matt Hancock is also being looked into for allegedly “lobbying” the watchdog to influence its findings in a Code of Conduct case.