Jess Phillips, the campaigning Labour MP, has been blocked from joining parliament’s sleaze watchdog after her own party withdrew its support.

The Birmingham Yardley MP’s name was printed on House of Commons order paper as a candidate to become the new member of the standards and privileges committee. But parliamentary sources have told the Guardian that support was dropped days ago after Labour’s officials indicated that other MPs were now interested in taking up the role.

One informed insider told the Guardian that Jeremy Corbyn’s office was behind the decision to drop Phillips – an outspoken critic of the Labour leader.

Corbyn has been under investigation by the parliamentary commissioner for standards, Kathryn Stone, for allegedly failing to declare flights. He has vigorously denied the claims.

Phillips criticised the appointment process, which sees party leaders and their whips given the power to nominate committee members.

“What worries me about the fact that my nomination was stopped is that it highlights that the current process is that party leaders have power over who goes on the standards committee – apart from the chair – and lays bare a flaw where once again political patronage and protection can subvert a process that now more than ever needs to be trusted,” she told PoliticsHome. Chairs are chosen by the committee members.

“Surely political parties could just fill it with yes men. I don’t think this has ever been the case, so I’m not sure why my nomination was withdrawn.”

A Labour source said other MPs have asked to be considered for the appointment following the vacancy created by Kevin Barron standing down as its chair. “This has nothing to do with any investigation. The investigation is being conducted by the commissioner for standards, not the committee on standards, and the committee is not involved in the commissioner’s decision-making,” the source said.

Corbyn was reported to Stone by Conservative MPs during the summer over allegations that he had not properly registered trips abroad which were paid for by other organisations.

Pictures had emerged of Corbyn holding a wreath in front of a plaque honouring the founder of Black September – the group behind the 1972 killing of Israeli athletes at the Munich Olympics – in Tunisia in 2014. The Labour leader said he was at the cemetery to pay his respects to the victims of an Israeli air strike in 1985.

Under new rules passed by the Commons in July, the details of all MPs under investigation by the independent watchdog are kept secret. However, the Guardian has been told that Stone’s office has made inquiries into the claims.

MPs must register foreign trips worth more than £300 if the costs have not been borne in full by the MP or public funds. Corbyn has said that he was confident all appropriate declarations were made.

The post of chair of the committee, which disciplines MPs for breaking parliamentary rules, became available in September after Barron stood down after eight years.

Corbyn’s office and Labour have been asked to comment.