Media said Nigel Evans, a lawmaker in Prime Minister David Cameron's Conservative Party, was being questioned over alleged attacks on two men in their twenties.
Evans, 55, is the Member of Parliament for Ribble Valley in Lancashire, northwest England as well as one of the House of Commons' three deputy speakers.
Lancashire Police said in a statement: "A 55-year-old man from Pendleton in Lancashire has today, Saturday, May 4 2013, been arrested by Lancashire Constabulary on suspicion of rape and sexual assault."
As a deputy speaker, the Welsh lawmaker can stand in in the absence of the speaker, whose job is to keep order during parliamentary debates.