LONDON — With their giddy celebrations of “independence day” having given way to political and economic turmoil, one thing has become especially clear about the former London mayor Boris Johnson and other leaders of the successful campaign to vote Britain out of the European Union: They had no plan for what comes next.

In the days since Britain voted to leave the bloc, the movement’s leaders have often appeared as if they had not expected to win and were not prepared to cope with the consequences. Faced with the scope of the decision, they have been busy walking back promises they made during the campaign and scaling back expectations. They have failed to show a united front or to answer basic questions.

Their faltering performance has added to the sense of political chaos in Britain and, arguably, to the turmoil in the financial markets. And it has undercut their credibility and authority as Mr. Johnson prepares his bid to become prime minister and lead Britain into a new relationship with the Continent.

The stakes are high for Mr. Johnson in particular, as he tries to build an impression as a capable leader amid the chaos that followed the vote in favor of a British exit, or “Brexit.” But the mixed signals coming from him and other proponents of leaving the European Union have left their intentions unclear on such basic issues as when and how they will seek to negotiate a withdrawal, and what kind of new arrangement they want. To the degree that they have signaled a direction, it has often been substantially different from what they promised during the campaign.