UK Prime Minister Theresa May could be barred from holding another vote on her Brexit deal.

In an explosive intervention, House of Commons Speaker John Bercow said on Monday that governments could not ask MPs to vote repeatedly on the same proposition.

"What the government cannot legitimately do is to resubmit the same proposition, or substantially the same proposition, as that of last week, which was rejected by 149 votes," Bercow told MPs.

The prime minister had been considering holding another meaningful vote this week.

LONDON — UK Prime Minister Theresa May cannot hold a third vote on her Brexit deal until there are significant changes to it, House of Commons Speaker John Bercow said on Monday.

In an explosive intervention, Bercow said that parliamentary precedent barred the government from holding repeated votes on the main motion. May had been considering holding another meaningful vote on her Brexit deal this week.

The Commons speaker cited a passage in Erskine May, the parliamentary handbook: "A motion or amendment which is the same, in substance, as a question which has been decided in the affirmative or negative during the current session may not be forwarded again during that session."

The speaker told members of Parliament that "what the government cannot legitimately do is to resubmit the same proposition, or substantially the same proposition, as that of last week, which was rejected by 149 votes."

The prime minister has already held two votes in the Commons on her Brexit deal, once in January and again on Tuesday. Both times MPs rejected it by huge margins.

Downing Street hopes that enough opponents to her deal with the European Union will be persuaded to back it now that face the prospect of a lengthy delay to Brexit.

Bercow said that the vote last week was permissible because the prime minister had added documents to the Brexit deal changed it substantially. But May cannot bring the deal back for another vote until there are significant changes to it, he concluded.

The EU has said it will not offer any new concessions on the withdrawal agreement, creating a huge headache for Downing Street, which is likely to challenge Bercow's position.

Hannah White, a deputy director of the Institute for Government think tank, said MPs could overrule convention if it were clear there was majority support for the deal.

White tweeted that while Bercow's ruling that a third meaningful vote "might fall foul of convention" that the Commons should not be asked the same question more than once in the same session, it "could still explicitly decide to set aside this convention I think if the Government could get a majority to vote for that."