George Osborne | Leon Neal/Getty Images George Osborne: Brexit doesn’t have to mean leaving customs union The former chancellor said he would ‘vigorously’ challenge the Brexiteers’ interpretation of the referendum result.

Leaving the EU does not necessarily mean the U.K. must leave the customs union or "radically" cut immigration, former Chancellor George Osborne told the BBC, adding that he would "vigorously challenge" the interpretation of the Brexit referendum result by Brexiteers.

Osborne — who also said he was amused by the "circus" going on beneath Theresa May over who would replace her — said that although he thought Brexit was wrong and he had opposed former Prime Minister David Cameron's decision to hold the referendum in the first place, he saw no prospect of the result being reversed.

But he said the manner of Brexit was very much up for grabs. "I will vigorously challenge how they [Brexiteers] want to interpret that result. I don’t accept that just because we’re leaving the EU we have to, for example, leave the customs union or radically clamp down on immigration," he said. The current government's position is that the U.K. should leave the single market and customs union when it quits the EU.

"How we leave, the new arrangements we have with Europe. How we allow people into this country to succeed … these are decisions that are up for grabs now in our parliamentary democracy in which every citizen in this country is entitled to have a view," he said.

Osborne told the Today program's guest editor, director of the English National Ballet, Tamara Rojo, that the referendum campaign leading up to the June 23 vote had made him gloomy about the result.

“I went round the country and I kept hearing from people I would assume wanted to stay in the EU that they wanted to leave. So I was pretty pessimistic and there was quite a lot of nervousness when I sat down that night in Downing Street to watch the outcome,” he said.

Once the result became clear, the former chancellor said he knew he was too strongly associated with the Remain campaign to put his hat in the ring for the top job. "I just didn’t think that I was in any position to unite the Conservative Party or indeed that I wanted to spend all my time and effort on a project that I didn’t believe in — which is taking Britain out of the EU," he said.

Now as editor of the Evening Standard, he said he enjoys watching the jockeying for position to succeed Theresa May. "Now of course from the chair of a newspaper editor I look with some amusement at the circus going on to see who will be the next Tory leader," he said, although he did not rule out a return to politics at some point. "I don’t rule out going back into politics, but it is certainly not plan A."