Hundreds of thousands of people opposed to Britain's withdrawal from the European Union marched through central London on Saturday to demand a new referendum as the deepening Brexit crisis risked sinking Prime Minister Theresa May's premiership.

After three years of tortuous debate, it is still uncertain how, when or even if Brexit will happen as Ms. May tries to plot a way out of the gravest political crisis in at least a generation.

Hundreds of thousands of people opposed to Britain's withdrawal from the European Union marched through central London on Saturday to demand a new referendum as the deepening Brexit crisis risked sinking Prime Minister Theresa May's premiership.

After three years of tortuous debate, it is still uncertain how, when or even if Brexit will happen as Ms. May tries to plot a way out of the gravest political crisis in at least a generation.