Despite the former Prime Minister, who stepped down after the referendum result in 2016, being staunchly Remain, he instead the approach by the European Parliament president is fundamentally wrong.
Juncker delivered his “State of the Union” speech in Strasbourg this week, in which he claimed the UK – and the EU – would regret Brexit.
Outlining what he claimed is a multitude of successes for the bloc, Juncker said Brussels has the “wind back in our sails”.
Juncker unashamedly called for closer ties in defence, budget and strategies throughout Europe, insisting with the recent wave of elections behind them, the EU is safe.
But speaking in Ukraine, at the Yalta European Strategy (YES) forum, Mr Cameron said the EU Juncker outlined was one he may have regrets about in the future.
He said: “The EU is making a mistake if they think simply because Macron had been elected and Angela Merkel will be elected (again) these problems will disappear.
“They haven’t. When Macron was elected there was a record vote for an unpleasant party.
“The worst thing to do is pretend populism doesn’t have real causes and real problems behind it.
“You have to make sure people don’t get left behind.”
Mr Juncker went off piste from his original speech on Wednesday, which declared the EU would have regrets over Brexit.
However, Mr Cameron said it was Brussels which will be left red faced if it arrogantly refuses to accept the troubles rocking the bloc.
Mr Cameron said the referendum in the UK was about the “growth of power of the EU” and the member state disagreeing with the spread of power, insisting Juncker needs to accept the fact.
He said: “If politicians in the EU think populism has gone away – that is a mistake.
“The problems are all still there. This is part of the problem with Mr Juncker’s speech.”
Mr Cameron said Mr Juncker was making “a mistake” in his speech in which he called for an ever closer union.
He said:”If your decision is going to be one all powerful presence, an EU army, tax rates imposed by major votes no variable speeds – that is a mistake.
“Are we going to give up being a reluctant tennant and try to be a happy neighbour?
“That is the approach we are taking. I don’t think Mr Juncker’s speech made that choice any easier.”
Because Marine Le Pen was defeated in Paris, and far right groups in the rest of Europe failed to win elections, Juncker and his Brussels allies are pushing ahead with a plan which will further tighten ties around the bloc.
Yet Mr Cameron believes this will cause a second wave of support for parties which buck the Brussels party line.
He said: “We have to look behind the rise of populism and stop politicians from simply complaining (about the rise).
“We have to understand the causes.
“There are two clear causes, while our economic systems deliver growth and prosperity, there are too many people left behind. The rising tide did not lift all boats.
“There are signs of people being left behind. The levels of immigration was too much for some people.
Despite political wrangling at home, and instance Brexit could fail, Mr Cameron insisted his Tory colleagues will carve out a role for Britain as a global leader once again.
He said: “Of course Britain voted to leave the EU, that doesn’t mean Britain will give up its global role.”