Britain's parliament must have a vote on an eventual agreement between the United Kingdom and the European Union on leaving the bloc, said a senior lawmaker who is chairman of parliament's Brexit committee.



Prime Minister Theresa May has said she will invoke Article 50 by the end of March next year, starting a two-year divorce procedure. She has said parliament will debate the government's plans but has ruled out a vote on triggering the divorce.



Hilary Benn, an opposition Labour Party lawmaker who will chair a newly formed committee set up to scrutinize government policy on leaving the EU, said on Thursday that it was "inconceivable" that lawmakers would not have a vote on the UK's final EU exit deal.



"I'm very clear that Parliament will want to have a say both in scrutinizing what the negotiating plan is when it is published, but also Parliament will want to take a decision on the final deal," Benn told BBC radio.



"It is inconceivable that Parliament shouldn't use its sovereignty... to determine what it thinks of the deal, this complex negotiation, when it is finally completed."



Campaigners have taken legal action to argue May and her ministers do not have the authority to invoke Article 50 of the EU Lisbon Treaty, the mechanism by which a nation can leave the bloc, without the explicit backing of parliament.



Britain's parliament will "very likely" have to ratify an eventual agreement with the European Union on leaving the bloc, a British government lawyer said on Tuesday.