John Bercow has torn into Boris Johnson, describing the prime minister as a "narcissist" who has "no redeeming virtues."
Speaking on The Great Debate on Monday evening, the former Speaker of the House of Commons said: "Never has a prime minister wielded so much power, made so little effective use of it, and been and been seen to be in quite such an indecent haste to blow his own trumpet."
"I've been aware of 12 prime ministers in my lifetime, by a country mile Boris Johnson is the worst.
"He's a narcissist. He doesn't do the detail. He's ritually dishonest, having a nodding acquaintance with the truth at best only in a leap year," Bercow also told host Trevor Phillips.
Bercow defected from the Conservatives to Labour last year, with the former Buckingham MP branding the Tories as "reactionary, populist, nationalistic" and also described Johnson as "a successful campaigner but a lousy governor" at the time.
Sign up to our newsletters here.