The prime minister could effectively overrule a bid to block a third vote on her Brexit deal with new legislation.
Theresa May is preparing to push for a third meaningful vote (MV3) on the withdrawal agreement she has struck with Brussels, which has twice been roundly defeated in the Commons.
Labour MP Chris Bryant is asking the Commons to bar the move on the basis of a little-known parliamentary convention, which says exactly the same question can’t be put to MPs over and over again.
Separately, Speaker John Bercow put himself on a collision course with the government on Wednesday when he said “a ruling would be made” on whether it was possible - suggesting he could use his own powers to intervene.
But Nikki da Costa, Downing Street’s former director of legislative affairs, said it would be “extraordinary” for Bercow to throw out a government motion. She added ministers could break the logjam by adding a new clause to the EU Withdrawal Act which forces a new vote.
The PM’s former parliamentary expert also said that if last-ditch talks with Brussels saw Attorney General Geoffrey Cox update legal advice on the Brexit deal, the motion could be viewed as asking MPs a new question and Bercow could come under pressure from MPs.
Da Costa told HuffPost UK: “The Speaker can’t just make a judgement on a government motion. That would be extraordinary.
“The question is whether MV3 is very similar to MV2. If the written legal advice has changed that would be helpful to the PM.
“If there are MPs saying publicly that they would like another say, then that would also suggest it [MV3] is something that the House favoured.
“There is also the politics of it. It would be very controversial for the Speaker to refuse.”
May’s ministers are making a desperate last-minute attempt to win over Tory Eurosceptics and the Democratic Unionist Party (DUP) as fears mount that MPs could thwart or drastically delay Britain’s exit.
MPs vote on Thursday on whether to delay the Article 50 deadline to give parliament time to thrash out a deal.
If a government motion was denied, da Costa said the PM could bring forward a new clause to add to the EU Withdrawal Act.
“In extremis, the government could look to adding to the EU Withdrawal Act bill at second reading,” she said.
“So, if the Speaker did, in the worst case scenario, refuse MV3, which would be absolutely extraordinary, then the legislation itself would have to include a new clause - section 30 of the EU Withdrawal Act.”
The prime minister’s official spokesman was asked whether Downing Street was concerned an MV3 motion could be ruled out.
“The procedures of parliament are a matter for the House,” the prime minister’s official spokesman has said.