Boris Johnson, one of the most high-profile campaigners for Britain to leave the European Union, told a national television audience that Britons should "take back control" and "prosper as never before" outside the EU.
There are two weeks to go to the referendum on Britain's membership in the 28-nation bloc, and opinion polls show it's a tight race between those who want to leave the EU - aka "Brexit" - and those who want to remain. If Britons opt for a British exit on June 23, it would be the first nation to withdraw from the bloc.
In a highly charged debate on ITV Johnson put forward his case for leaving alongside fellow "Brexiters" Andrea Leadsom, a Conservative MP, and Gisela Stuart, a Labour Party politician.
They were opposed by Nicola Sturgeon, the First Minister of Scotland, Angela Eagle, a senior Labour Party politician, and Amber Rudd, a Conservative MP and Britain's Energy Secretary.
Although there have been several EU referendum television specials, this was the first major head-to-head debate, and it was undoubtedly a big test for Johnson.
The former Mayor of London is seen as one of the favourites to succeed Prime Minister David Cameron, who is on the opposite side of the debate. If the majority of voters side with Johnson and vote to leave the EU, there will likely be calls for Cameron to step down.
During the debate, Johnson was repeatedly accused of being driven by personal ambition.
"Boris is only interested in David Cameron's job," said Sturgeon.
Rudd said: "The only number Boris is interested in is the one that says Number 10."
Johnson insisted that Britain leaving the EU was the only way to claw back sovereignty and regain control of the country's borders. As a member of the EU, Britain has to abide by freedom-of-movement rules and can't block entry by citizens from the bloc.
Britain has "absolutely no way of controlling" the flows of immigrants coming into the country, he said.
The six politicians clashed on issues including immigration, the economy, and the National Health Service. Those arguing to remain in the EU were keen to steer the debate toward issues on the economy, those who were pro-Brexit repeatedly returned to issues around immigration.
Tempers also flared over a claim from the Brexit camp that Britain sends 350 million ($712 million) a week to the EU - a claim emblazoned across the campaigners' battle bus. Critics say that the claim doesn't take into account the rebate and subsidies Britain gets back. Sturgeon said that Johnson was driving around Britain in a bus with a "giant whopper" painted on the side.
When Sturgeon was pressed on what a Brexit result could mean for a second independence referendum in Scotland, she said that the issue was "speculation".
Yesterday former prime ministers Tony Blair (Labour) and John Major (Conservative) shared a platform in Northern Ireland to argue that at stake was the very existence of Britain itself.
They said that a Brexit result could trigger a second referendum on Scottish independence, and could disrupt stability in Northern Ireland. "The plain, uncomfortable truth is that the unity of the United Kingdom itself is on the ballot paper in two weeks' time," Major said.