LONDON — British lawmakers passed a measure on Thursday to stop the next prime minister from suspending Parliament to force through a no-deal Brexit, delivering a strong rebuke to Boris Johnson’s hard-line strategy.
With a 315 to 274 vote, support for the proposal was stronger than many had expected in the ranks of Conservative lawmakers. That puts Parliament on a collision course with Mr. Johnson, who is likely to succeed Prime Minister Theresa May next week and has entertained the idea of shutting down the legislature in the fall to ensure Britain leaves the European Union on Oct. 31, with or without a deal.
Opinion is split about whether the maneuver fully blocks a suspension of Parliament, but the size of the victory will embolden opponents of a no-deal Brexit and strengthen the arguments of some on Mr. Johnson’s team who would prefer to avoid suspending Parliament.
Opponents of a no-deal Brexit, desperate to find a way to push their plan through, attached it to a bill related to Northern Ireland, which is awaiting approval. Their amendment requires lawmakers to have a chance every two weeks to debate efforts to restore Northern Ireland’s paralyzed regional government.
It also requires Parliament to be reconvened for five days in October, even if the next prime minister suspends the body.
Although the government officially opposed the amendment, several members of Mrs. May’s cabinet abstained on the question, signaling tacit support of the proposal and daring Mrs. May to fire them. Mrs. May herself opposes a no-deal Brexit, but she has resisted lawmakers’ attempts to increase their powers to stop it from happening.
If he becomes prime minister as expected, Mr. Johnson has promised to negotiate a radically rewritten deal with the European Union by Oct. 31, or to leave without a deal on that date if he cannot. He would most likely need to circumvent Parliament to secure a no-deal Brexit.
Anti-Brexit lawmakers greeted the vote as a major defeat for Mr. Johnson and said it improved the chances of a second Brexit referendum, though opposition to that move is also widespread in Parliament.