Gina Miller, who took the British government to court over triggering Brexit, said if Britain leaves the European Union next year all sides must accept the result and the campaign to remain in the bloc should be abandoned.
More than two years since the 2016 EU referendum, the United Kingdom, its politicians and its business leaders remain deeply divided over Brexit while Prime Minister Theresa May has yet to clinch a divorce deal with the EU.
Opponents of Brexit are exploring ways to stop what they say is Britain's biggest mistake since World War Two.
Miller is leading a campaign to have another referendum, but she said if the government manages to successfully navigate an exit deal then politicians must be allowed to focus on domestic issues without the distractions of a debate about Britain's relationship with Europe.
"Whatever happens at the end of the Brexit process we have got to draw a line under it," Miller told Reuters on Friday in an interview in Mayfair in central London.
"Everyone is obsessed. Our bandwidth is completely taken up with Brexit. Our money, our time... We can't carry on like this. We need to make the best of it."
The complexity of delivering Brexit has sapped the government's time as officials focus on creating new systems for policing immigration and customs, settling the rights of citizens in each other's countries, negotiating a potential exit bill and preparing to strike new trade deals.
Miller, who co-founded an investment management company and campaigns for transparency in the industry, is one of the most outspoken campaigners on Brexit, best known for successfully taking the government to the Supreme Court to challenge its authority to leave the EU without a vote in parliament.
Brexit reversed?
She now wants a rerun of the 2016 EU referendum, this time offering voters the option of leaving on the terms of May’s deal or staying in a reformed EU.
She has been vilified in the pro-Brexit media and faced death threats, harassment and racial abuse for her views.
Opinion polls show Britain remains deeply divided over Brexit, though some recent surveys have shown a swing towards support for staying in the EU.
While pro-EU supporters have praised Miller, opponents have cast her as a wealthy member of an establishment which wants to soften or slow Brexit in defiance of the wishes of the people.
Campaigners on both sides of the argument have been stepping up their efforts in recent weeks as some Brexiteers argue for a cleaner break from the EU and Remainers say ending membership as currently planned would do economic damage to Britain.
Miller says it is "very likely" Britain will need to hold a second referendum on EU membership or a general election to break the deadlock over Brexit.
Some eurosceptic rebels in May's party and opposition parties have publicly said they will oppose the prime minister's plans to leave the EU.
If the opposition parties and just over a dozen rebels in May's party vote against a deal, she would fall short of the majority needed to get her deal through parliament.
This would plunge British politics into crisis and increase the likelihood that Britain would face leaving the EU without an agreement or face the possibility of another general election or a second referendum.
"There's no way out other than to give it back to the people," Miller said. "It is only morally and democratically right to give people a say."
Miller said, though, if the government does eventually pass a deal then she is not interested in leading a campaign for Britain to re-enter the EU in the future.
She would instead like to campaign on other constitutional issues like devolving policy and government spending away from London to the rest of the United Kingdom.
"At what point do you need to say that the country needs to get on with being a country? You can't have a nation living in stress," Miller said. "Whatever happens there has to be an amnesty."