Campaigning MP Tom Watson is at the centre of a huge row over his refusal to quit from the influential Commons committee investigating the phone hacking scandal.
The Black Country MP could face the judgment of senior MPs after he refused to back down over demands for his resignation.
Mr Watson (Lab West Bromwich East) has used his role as a member of the Commons Culture, Media and Sport Select Committee to expose the scandal of phone hacking by journalists on the News Of The World and other newspapers.
He was one of the MPs quizzing newspaper boss Rupert Murdoch when Mr Murdoch was attacked by a protester wielding a custard pie in July.
But he now faces demands to quit after accepting a job in Labour leader Ed Miliband’s shadow cabinet team.
Mr Miliband made Mr Watson Labour’s Party Deputy Chair and Campaign Co-ordinator earlier this month.
And Tory MP John Whittingdale, chairman of the Culture, Media and Sport Committee, has insisted Mr Watson must stand down – claiming he can’t be an independent member of the committee when he also has an important job in Labour’s top team.
Now, Mr Whittingdale is threatening to take his complaints about Mr Watson to a committee of the most senior MPs, called the Liaison Committee.
In an interview with magazine Total Politics, Mr Whittingdale said: “There’s a convention that select committees should be obviously independent and that membership should be confined to backbenchers.
"That’s a sensible convention, and I do think that there are potential conflicts for members who hold frontbench responsibilities.”
Asked what he would do if Mr Watson refused to resign, Mr Whittingdale said: “It’s early days, but I think if he was determined not to stand down, it may be that the liaison committee would take a view.”
But Mr Watson said: “It wouldn’t surprise me if this is a result of the higher echelons of the Conservative Party putting pressure on John Whittingdale.
“I’m not a front bench spokesman. I’m my own man. Nothing will deter me from getting to the truth behind this scandal. I would resign from the shadow cabinet before resigning from the select committee.”
The MP returned this weekend from attending the annual general meeting of Mr Murdoch’s business News Corporation in Los Angeles.
There, he told Mr Murdoch police were investigating allegations that private investigators employed by the newspaper group hacked computers.