Home Secretary Theresa May, the frontrunner in the contest to be Britain's next prime minister, said on Sunday the United Kingdom had to be clear about its negotiating stance on a post-Brexit deal with the European Union before triggering article 50.

Britons voted to leave the bloc in a referendum on June 23, prompting Prime Minister David Cameron to resign after he had led the campaign for a "Remain" vote.

Cameron has said his successor would have to decide when to trigger article 50, the formal step that will begin the process of negotiating the terms of Britain's exit.