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George Osborne, the chancellor of the Exchequer and effectively the No. 2 official in the British government, saw his prospects of ever becoming prime minister dim last Thursday when Britain voted to leave the European Union.

Mr. Osborne, a close ally of Prime Minister David Cameron, had campaigned vigorously for Britain to remain in the bloc.

Mr. Cameron announced on Friday that he would step down by October, and Mr. Osborne told the BBC on Tuesday that he would not join the race to succeed him as prime minister.

I don’t see how I could be the person to bring the party together.

The most likely successors to Mr. Cameron include Boris Johnson, the former London mayor who was one of the most prominent faces of the campaign to leave the European Union, and Theresa May, the home secretary, who supported remaining in the 28-nation zone.

The health secretary, Jeremy Hunt, another possible contender, told the BBC on Tuesday that he was “seriously considering” putting his name to lead the Conservative Party and that he thought the British people deserved a chance to weigh in on Britain’s relationship with Europe — either through another referendum or in an early general election.

Mr. Osborne, at a conference of business executives, said his focus was on steering Britain’s economy through the turmoil.

“My message today is both one of realism and reassurance: realism about the economic challenge that the country now faces, and reassurance that we are about as well placed as we possibly could be as an economy to meet that challenge.”

He called the referendum a “huge exercise in democracy” and reiterated statements he made before the markets opened on Monday: The government and the Bank of England had put in place contingency plans to stabilize the economy, including the financial sector, a major part of Britain’s economy in general and London’s in particular.

It was “nonsensical,” Mr. Osborne said, for some to suggest that the government should have had a full plan for leaving the European Union. “What is the case is that we in the Treasury and the Foreign Office and the government in general did set out the kind of options that are available for the United Kingdom outside of the European Union,” he said.

Those options include the possibility that, while leaving the European Union, Britain might remain part of the European Economic Area, or maintain separate trade arrangements with European countries via its participation in the World Trade Organization.

“What we were unable to do, of course, as the people arguing strongly for ‘Remain,’ was decide what option the country should choose,” he said. “That’s got to now be a collective discussion, a collective discussion within the governing party, a collective discussion within Parliament.”

Mr. Osborne added: “We, in my view, should move toward an arrangement that provides us with the closest possible economic ties to our neighbors.”

Mr. Osborne said that he agreed with Mr. Cameron that “until we are clear about that model, we should not trigger the Article 50,” the treaty provision that would formally start Britain’s withdrawal from the European Union.

Of his own political future, Mr. Osborne said: “I gave everything to this campaign. I don’t do things by half-measure. I passionately believe it would be a mistake for us to quit the E.U. I argued for us to remain.”

Given that his side lost, he said, “I don’t see how I could be the person to bring the party together.”

He added: “I love this country, right or wrong, and I’m going to be giving 100 percent to making this work for Britain.”

Mr. Osborne did not rule out continuing in government under the next prime minister.

“I’ve given much of my adult life to public service,” said Mr. Osborne, 45, who was elected to Parliament in 2001, when the Conservative Party was in the opposition. “This is the biggest political challenge the country has faced in my lifetime, and it would not be right, I think, for me just to walk away. How I can serve the Conservative Party is for the next leader to decide.”

He said he hoped Britain would maintain access to the European Union’s common market — the world’s largest trading zone — and that London would continue to be a hub for the trading of euro-denominated securities. But he noted that much remained unresolved, because “the smoke is only beginning to clear from the battlefield.”