Labour leader Jeremy Corbyn has likened Theresa May to the comedy character Baldrick over her approach to Brexit negotiations, telling MPs her "cunning plan is to have no plan".
He said the prime minister's position owed less to "great philosophers" than the hapless sidekick from the 1980s BBC TV show Blackadder.
Mrs May noted Sir Tony Robinson, who played Baldrick, was a Labour member.
Sir Tony later described the pair as "a beardy man and a grumpy lady".
During Prime Minister's Questions, Mr Corbyn and Mrs May argued over the government's yet-to-be-announced stance for when negotiations for leaving the European Union begin next year.
The Labour leader accused the prime minister of presiding over a "shambolic Tory Brexit" and called for clarity and warned of the effect of it might have on the Irish border.
Mrs May pledged no return to the "borders of the past", saying a Common Travel Area had existed since 1923, and accused Mr Corbyn of trying to "frustrate the will of the British people" over the EU referendum.
The government has said it will formally trigger Brexit talks by the end of next March, but has consistently refused to offer a "running commentary" on its negotiating stance.
Prime Minister's Questions took an unusual turn when Mr Corbyn made reference to Baldrick, the turnip-loving and intellectually challenged servant to Rowan Atkinson's 1980s historical comedy character Edmund Blackadder.
He said: "When you're searching for the real meaning and the importance behind the prime minister's statement (on the recent European Council summit), you have to consult the great philosophers.
"The only one I could come up with is Baldrick, who says, 'Our cunning plan is to have no plan."'
This was a reference to Baldrick's frequent claim to have a "cunning plan" to deal with the trickiest situations, but which nearly always turned out to be less than brilliant.
Mrs May responded: "I'm interested that you chose Baldrick. Of course, the actor playing Baldrick was a member of the Labour Party, as I recall."
Sir Tony is a long-serving activist who has chaired proceedings at the party's annual conference - he has also been a recent critic of Jeremy Corbyn's leadership.
The reference prompted him to tweet, mocking Mrs May's oft-used pledge that "Brexit means Brexit", by saying "Baldrick means Baldrick".
"I'm in the hairdresser's," he later added. "Suddenly a lot of people seem to want to talk to me!"
Returning to his put-upon alter-ego, he wrote: "I never said nuffin' at PMQs, it was the beardy man and the grumpy lady. Baldrick x"