LONDON (AP) — In Brussels and London, one question is growing louder: Can Boris Johnson be stopped?

Britain’s prime minister says the U.K. is leaving the European Union in less than 90 days, with or without a divorce deal.

Pro-EU British lawmakers are gearing up for a final effort to prevent a no-deal Brexit. But it’s not clear whether Parliament can halt a prime minister who insists the U.K. will leave on Oct. 31 “come what may.”

Constitutional expert Vernon Bogdanor says doing that will be “very, very difficult.”

Britain and the bloc, meanwhile, are accusing each other of torpedoing talks. British Cabinet minister Michael Gove accused the EU on Tuesday of “refusing to negotiate with the U.K.”

The EU said its door was open “should the United Kingdom wish to hold talks.”