But, after a momentous court ruling delivered Thursday
, Prime Minister Theresa May has lost some of the control she enjoyed. Instead, a London-based businesswoman and philanthropist has seized the momentum.
Gina Miller is the lead claimant in a historic action that thwarted the UK government's plans to trigger Article 50 of the Lisbon Treaty -- starting the formal process of Britain leaving the European Union -- without a vote in Parliament.
Miller's victory means that the Brexit process can't begin until UK lawmakers have had their say -- likely adding yet more frustration and delay to a government that has yet to lay out its clear plan for Brexit.
But who is Miller? Why is she taking on May and the Brexiteers -- and has she won?
Miller, an investment banker, revealed she was "physically sick"
on the night of EU referendum as 17.4 million voted leave.
But by the next morning she was already planning to take on the government to ensure that the Prime minister could not invoke Article 50 without a vote in Parliament.
Miller, who was born in Guyana but lived in the UK for the past 41 years since the age of 10, runs an investment company with her husband, Alan.
As well as helping consumers and businesses, she and her husband have both given thousands of pounds to charities in the UK, including the Lady Thatcher infirmary at the Royal Hospital Chelsea.
What she said
Miller, who brought the case with hairdresser Deir Dos Santos, said she was delighted after the court ruled that members of parliament must be given a say in the process of leaving the EU.
"This result today is about all of us: our United Kingdom and our futures," Miller said in a statement.
"It is not about how any of us voted -- each of us voted to do what we believed was the right thing for our country.
"This case is about process, not politics. My dedicated legal team -- Mishcon de Reya and counsel -- are, alongside myself and my supporters, pleased to have played our part in helping form a debate on whether the rights conferred on UK citizens through Parliament legislation 44 years ago could be casually snuffed out by the Executive without Parliament or our elected representatives and without proper prior consultation about the Government's intentions for Brexit.
"However you voted on 23 June, we all owe it to our country to uphold the highest standards of transparency and democratic accountability that we are admired and respected for around the world."
While Miller has won plaudits for taking her case to court, she has also been the subject of vicious online trolling.
Who else is involved?
While Miller was the lead claimant, she was not alone in challenging the government.
The People's Challenge, which was financed through a crowd funding campaign, raised £175,550 ($218,551) to help finance the case.
Grahame Pigney, who was part of the campaign, "welcomed the decision as "the alternative would have meant a horrifying executive power grab that has no place in a modern democracy."
He added: "We started this challenge in order to protect parliamentary sovereignty and the rights of millions of UK Citizens; the Court's decision has justified our action. Hopefully the debate on and passing of primary legislation by Parliament will result in a more positive and less divisive way forward for the UK."
What happens now?
The UK government has already said it will appeal the decision at the UK Supreme Court and added that it remains committed to invoking Article 50 by the end of March.
"The country voted to leave the European Union in a referendum approved by Act of Parliament. And the government is determined to respect the result of the referendum," a government spokesperson said.
Experts say parliament is unlikely to block the triggering of Article 50 outright. But the ruling could mean it is delayed, particularly by opposition in the upper chamber -- the House of Lords.
It may give lawmakers the opportunity to influence what kind of deal the government negotiates with the EU.
Britain's Supreme Court is likely to hear the appeal in early December.