Cameron told a gathering of students at DePauw University in Indiana, US, about his concerns over the Euro, and said: “It is not working as it was intended.”

In his first major speech since resigning at the Tory leader, Cameron said: “I see more trouble ahead… I wonder how long it can last.

“Some countries have seen decades of lost growth – those countries have a single currency but they don’t have a single fiscal system, a fiscal tax system. It creates bigger differences.”

“You in the United States have ways to make sure that if you have a bad year you pay less in taxes and offset federal programmes. There are no such arrangements in Europe.”

However, the Remoaner still appears optimistic about the EU, saying he didn’t think other countries would follow Britain out of the European bloc.

He predicted France would not vote for right-wing leader Marine Le Pen in next year’s presidential elections while he also thought Geert Wilders would not be victorious in the Netherlands.

The former Conservative leader also considered the similarities between Brexit and Donald Trump’s landmark election win, claiming they both came about as a result of Britons and Americans feeling left behind in a rapidly-changing world.

He said: “We know that immigration has benefited both our countries, but we need a system of control.

“And we may not need a wall, but we do need borders that work and are seen to work. We need that in Europe, just as in the United States.”

Urging President-elect Trump to avoid protectionist policies when he takes over the Oval Office next year, Cameron said the US should be wary of the kind of legislation that could hamper the growth of emerging industries.

The former PM later tweeted from a college basketball game where he was joined by ex-US President George W. Bush.