Deputy House of Commons Speaker Nigel Evans has been arrested on suspicion of rape and sexual assault, Press Association sources say.
The 55-year-old Conservative MP is being questioned about alleged attacks on two men in their 20s, the sources said.
Police said a 55-year-old man was being interviewed by officers.
The alleged offences took place between July 2009 and March 2013 in Pendleton, Lancashire, police added.
In a statement, a Lancashire Constabulary spokesman said: "A 55-year-old man from Pendleton in Lancashire has today, Saturday, 4th May 2013, been arrested by Lancashire Constabulary on suspicion of rape and sexual assault.
"The man will be interviewed at a police station in Lancashire during the course of the day.
"The offences are alleged to have been committed in Pendleton between July 2009 and March 2013.
"We take all allegations of a sexual nature extremely seriously and understand how difficult it can be for victims to have the confidence to come forward.
"As a constabulary, we are committed to investigating sexual offences sensitively but robustly recognising the impact that these types of crimes have on victims.
"We would encourage anyone who has experienced sexual abuse, or who has information about it, to have the confidence to report it to us knowing that we will take it seriously, deal with it sensitively and investigate it thoroughly."
Mr Evans, MP for Ribble Valley since 1992, was elected one of three Commons deputy speakers three years ago.
BBC political correspondent Iain Watson described him as gregarious, energetic and well-liked across the political spectrum.
In more than two decades, the Swansea-born MP has held some senior posts in the party, including shadow Welsh secretary.