The Labour MP Dawn Butler was absolutely correct to call Boris Johnson a liar in the Commons, Keir Starmer has said, saying the prime minister was “the master of untruth and half-truths”. It comes as John Bercow, the former Speaker, argued for a change to Commons rules barring MPs from calling each other liars, saying this was “the product of a bygone age” where politicians were more scrupulous about honesty. Butler was ejected from the chamber on Friday when she said Johnson had lied repeatedly to fellow parliamentarians and the country, and refused to withdraw the remark. Starmer, however, also backed the actions of the stand-in deputy speaker, Judith Cummins – another Labour MP – in suspending Butler for the day, saying Cummins had no choice as parliamentary rules barred MPs from accusing each other of dishonesty. “Poor people in this country have paid with their lives because the prime minister spent the last 18 months misleading this house and the country,” Butler had told the Commons. Asked about the Brent Central MP’s remarks, Starmer told LBC: “I agree with what Dawn had to say. The prime minister is the master of untruth and half-truths. And Dawn was simply giving some examples of that. “I think there’s a lot of people that feel that it’s the person who’s not telling the truth rather than the person who’s calling it out that ought to be on the hot spot, so I agree with Dawn on that.” The Labour leader added: “But I do want, in fairness to the temporary Speaker, Judith Cummins, who was there – she did the right thing, she followed the rules, because parliament doesn’t allow you to call other parliamentarians liars in the chamber. So I don’t criticise the deputy speaker for what she did. But do I support Dawn in what she said? I absolutely do.” In an article for the Times jointly written with Butler, Bercow said the rules should be changed. They wrote: “The brutal reality is that the rules are the product of a bygone age when all honourable members sought conscientiously to tell the truth and would quickly apologise and correct the record if they inadvertently misled the house. This prime minister – and, indeed this government – have no such scruples.” Speaking in a backbench business debate shortly before the end of the final day of Commons business before the summer recess, Butler cited incidents including the prime minister’s comment to MPs earlier in the month that the Covid vaccination programme had “severed” the link between infections and serious illness or death. Butler told MPs: “Not only is this not true, it’s dangerous. It’s dangerous to lie in the pandemic. And I’m disappointed the prime minister has not come to the house to correct the record, and to correct the fact that he has lied to this house and the country over and over again.” Cummins, who was filling in as deputy speaker after one of the office-holders, Rosie Winterton, was forced to self-isolate, intervened twice to ask Butler to withdraw the charge of lying, but Butler refused.