Sir Keir Starmer has warned backbench Labour MPs against future rebellions as he seeks to restamp his authority on the party after a series of setbacks.
The prime minister suffered the biggest rebellion of his premiership over his plans to cut benefits by billions, climbing down at the last minute amid fears his majority could be overturned.
In the end, 47 Labour MPs voted against the welfare bill at its final Commons hurdle.
And chief whip Sir Alan Campbell wrote to rebels on Wednesday to remind them of their votes against the measures.
In a letter seen by The Times, Sir Alan said: “I am writing about your vote in the above divisions. As you know, it is against the standing orders of the PLP [parliamentary Labour party] to vote contrary to the frontbench position, and in so doing therefore you have broken the whip.”
Sir Keir has also suspended four Labour MPs for their roles in the rebellion and other breaches of party discipline.
One rebel Labour MP, Jon Trickett, wrote on X that he did not regret having voted against the government. He said: “Today, along with other rebels, I got an email from party authorities telling me I voted in parliament against the government’s welfare reforms six times in one day.
“I don’t repent my votes. I was elected on a pledge to stand by working-class electors and above all the poorest.”
Another Labour MP described the letter as a “shot across the bows” as Sir Keir tries to shore up his authority.
But the move is unlikely to be welcomed by MPs, who have been outspoken about the prime minister’s engagement with his backbenchers.
A large chunk of Labour’s parliamentary ranks feel Sir Keir failed to listen to and address concerns among MPs about the cuts to the personal independence payment (Pip), and that the eventual U-turn was a self-inflicted error.
The U-turn has left Rachel Reeves with a £5bn hole to fill ahead of this autumn’s Budget, with the chancellor likely to hike taxes to plug the gap.
But Labour’s manifesto pledge not to raise taxes on “working people” leaves the chancellor with a limited number of workable options.
There have been calls from Labour MPs on the left of the party to introduce a wealth tax, calls which have only grown in the wake of Tuesday’s welfare climbdown.
Rachael Maskell, the now-suspended architect of the rebellion which forced the government into shelving key pillars of the bill, demanded the government increase taxes on the very richest to pay for the £5bn climbdown.
