Conservative MP Andrew Bridgen has accused the Speaker of "defending the indefensible" in a heated Commons exchange.
The pair became embroiled in a spat following a debate on a Standards Committee's report on the case of Labour MP Keith Vaz, who was found to have "expressed willingness" to purchase cocaine for male prostitutes.
The Leicester East MP has consequently been given a six month Commons suspension.
But Mr Bridgen criticised John Bercow's "very close relationship" with Mr Vaz, and his failure to condemn the MP.
"It is clear to me, and it'll be clear to the public that to the fag-end of your tenure in that chair, you are defending the indefensible," he said.
"The House can come to its own conclusion, the Standards Committee has come to its own, and Mr Speaker, the public will come to theirs."
Hitting back at Mr Bridgen, Mr Bercow said trying to "smear" him would get him "the square root of nowhere", arguing he is not involved with complaints regarding the behaviour of MPs.
"I am friendly with the member for Leicester East, as I'm friendly with the member for Christchurch, Aylesbury, Stroud and Strangford. I am friendly with a great many members having served in this place for 22 years," he said.
"I do not get involved in matters appertaining to standards."
In a statement on his website, Mr Vaz said he denied the allegations against him.
"Mr Vaz has never bought, possessed, dealt with or used illegal drugs," it read.
"He has a cardiovascular condition which would mean that were he to consume any non-prescribed drugs he would in all likelihood die."
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