Two days after Prime Minister David Cameron resigned over his failure to keep Britain in the European Union, Labour leader Jeremy Corbyn faced a revolt by his lawmakers who called for him, too, to quit.
US Secretary of State John Kerry will also fly first to Brussels and then onto London on Monday, amid dismay in Washington over Britain's decision.
European leaders have called for a swift divorce amid fears of a domino-effect of exit votes in eurosceptic member states that could imperil the integrity of the 28-country alliance.