Liz Truss has sacked trade minister Conor Burns from her government “with immediate effect” following an allegation of serious misconduct.
The Tory MP for Bournemouth West has also had the whip suspended while the complaint is investigated.
A No 10 spokesman said: “Following a complaint of serious misconduct, the prime minister has asked Conor Burns MP to leave the government with immediate effect.
“The prime minister took direct action on being informed of this allegation and is clear that all ministers should maintain the high standards of behaviour – as the public rightly expects.”
A whips office spokesman said: “We have suspended the whip pending investigation into allegations of inappropriate behaviour earlier this week.
“We take all such allegations extremely seriously. The prime minister has been clear that the highest standards in public life must be upheld.”
It comes after the annual Conservative Party conference took place in Birmingham from last Sunday to Wednesday.
Mr Burns, who has held the seat since 2010, has said he will co-operate fully with the probe and “looks forward to clearing his name”, according to The Sun.