LONDON — Four days after a decisive vote to leave the European Union, Britain was consumed on Monday with questions of when and how the country’s departure from the bloc would happen — and increasingly, of whether it would happen at all.

The immediate outcome of Thursday’s referendum was not the promised clarity but an epic political muddle and a policy vacuum that invited more confusion and turmoil throughout the day in Britain, on the Continent and in the financial markets.

Leaders on both sides of the Channel said there was no viable option but to move gradually toward the withdrawal process. Yet the day’s developments did little to dispel the possibility that the crisis could drag on for a long time, possibly generating enough economic and political damage to encourage negotiation of a new arrangement between Europe and Britain that would sidestep the need for a formal withdrawal or at least minimize its effects.

Prime Minister David Cameron and leaders of the campaign to leave stuck to their positions that they would not move quickly to begin formal talks on withdrawal, even as European leaders turned up the pressure on Britain to get on with it.