MP Dan Norris has been arrested on suspicion of rape, child sex offences, child abduction and misconduct in a public office.
The Labour Party says it "immediately suspended" the MP for North East Somerset and Hanham after being made aware of his arrest.
Avon and Somerst Police confirmed that a man in his 60s was arrested on Friday and released on conditional bail.
Norris, 65, was elected as the MP for North East Somerset and Hanham in 2024, defeating the Conservative MP Jacob Rees-Mogg.
He had previously been in Parliament from 1997 to 2010 representing the seat of Wansdyke.
In a statement, Avon and Somerset Police said: "In December 2024, we received a referral from another police force relating to alleged non-recent child sex offences having been committed against a girl.
"Most of the offences are alleged to have occurred in the 2000s but we're also investigating an alleged offence of rape from the 2020s.
"An investigation, led by officers within Operation Bluestone, our dedicated rape and serious sexual assault investigation team, remains ongoing and at an early stage.
https://www.bbc.com/news/articles/czx48gq0y77o