Cameron began the day alongside senior Conservative party leader and former PM Sir John Major and former Labour party leader Harriet Harman in Bristol today,the last official day of campaigning before polling booths open tomorrow morning.
"You can't jump out of the aeroplane and then clamber back through the cockpit hatch," he warned those contemplating Brexit - or Britain's exit from the 28-nation economic bloc.
Earlier speaking to the BBC, Cameron had reiterated the case for Remain that the UK enjoyed a "special status" within the EU and the "best of both worlds".
"The idea you have to choose between being a success in the European single market of 500 million and campaigning to have jobs and wealth created by trading with other economies - you don't have to choose, you should do both.
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"We're in that single market, we're driving that single market, there are lots of things that Britain can help Europe to achieve - whether it's tackling terrorism or signing better trade deals in the future - but we have our own special status protected."
"We have not been invaded for 1,000 years, we've got institutions that have served us well. I don't want to give that up to some sort of 'United Europe' and that's not what we're going to do.
"We're out of the euro, out of ever-closer union, we're proud Brits and really proud of what our country can achieve, but, frankly, we achieve more if we're in these organisations fighting for British interests and British values rather than standing outside for them," he said.
London mayor Sadiq Khan, a key Remain supporter, accused his predecessor Boris Johnson of changing his mind over the benefits of the EU to businesses.
"The problem is this, Boris. You might start off by saying how wonderful immigration is. But your campaign hasn't been Project Fear, it's been Project Hate as far as immigration is concerned,"he told Johnson.
The resultwillbe declared by Jenny Watson, the chair of the UK's Electoral Commission and thereferendum's chief counting officer at Manchester Town Hall on Friday morning.