Chris Law’s (Dundee West) cheeky remark prompted an intervention from Commons Speaker Sir Lindsay Hoyle, with a plea to consider the “pride of this Parliament”.
Mr Law subsequently amended his remark to say “bottom” instead.
The SNP MP was speaking at Prime Minister’s Questions (PMQs), where he hit out at Labour for not committing to scrap the so-called bedroom tax and the two-child benefit cap.
The under-occupation deduction, described by opponents as the bedroom tax, sees benefit claimants have their payments reduced if they have an unoccupied bedroom.
Mr Law described them as the “cruellest of Westminster policies”, adding: “Astonishingly we have learned over the summer the leader of the opposition is an enthusiastic supporter of these Tory cruel welfare policies, with U-turn after U-turn from the Labour Party.
“So given that the Tories and Labour are two cheeks of the same arse, offering no change, no vision, no hope, does the Prime Minister agree that the only way Scottish voters can…”
Commons Speaker Sir Lindsay Hoyle interrupted to say “let’s think about language”, and raised the importance of the “pride of this Parliament”.
Mr Law continued: “Happy to change the offending word with ‘bottom’.”
And he finished his question, asking the Prime Minister if the way to avoid such policies is for people in Scotland to vote for his party and leave the union.
The Prime Minister added: “We want to ensure a welfare system that is compassionate and looks after the most vulnerable in our society whilst supporting those who can (get) into work to do so, because that’s also fair for everyone else.”
Shadow chancellor Rachel Reeves did not rule out maintaining the two welfare policies if Labour was in power, citing the economic situation her party could inherit if elected.
Mr Law’s was not the only reference of its kind at PMQs, with other MPs making reference to minsters’ “posteriors”.
Earlier in the session, Labour MP Andy McDonald (Middlesbrough) hit out at investment in schools, saying a school in his constituency needs a new building so pupils don’t have to use temporary accommodation, saying: “Can the Prime Minister and his Education Secretary (Gillian Keegan) get off their derrieres and sort this out.”
And Labour MP Mary Glindon (North Tyneside) said “we’ve heard far too much lately about ministerial posteriors”.
The remark was an apparent reference to earlier in the week when Education Secretary Gillian Keegan was forced to apologise after railing against those who she said had “sat on their arse and done nothing” about reinforced autoclaved aerated concrete (Raac) in a sweary outburst on Monday.
SNP leader Stephen Flynn used his opportunity at PMQs to also reference the remark, outlining issues around the cost of living and the economic situation, saying: “So can I ask the Prime Minister: when is he going to get off his backside and do something about it?”
Mr Sunak said new figures showed “we had the fastest recovery out of any European economy after Covid”.