Conservative MP Philip Davies has submitted a letter of no confidence in Theresa May's leadership, saying that he has "lost trust" in her ability to deliver Brexit.
Mrs May could face a confidence vote if the chairman of the backbench 1922 Committee Sir Graham Brady receives letters from 48 Tory MPs. It is not known how many he has so far received.
In a letter to voters in his Shipley constituency, obtained by the Yorkshire Post, Mr Davies said that Mrs May's Chequers plan for Brexit was "unacceptable".
And he added: "Politics is all about trust and once it is lost it is impossible to win back. Many people have told me that as a result of this they have lost trust in the PM to properly and fully deliver the referendum result. It is with much sadness that I have to say that I have also lost trust in her to deliver the referendum result too."