David Cameron is a Eurosceptic who would be campaigning for Britain to leave the EU if he was not prime minister, Steve Hilton has claimed. The remarks from Cameron's former most senior adviser come ahead of a four-week purdah, which will take effect from tomorrow (27 May) to ensure civil servants remain neutral.

"If he was a member of the public, or a backbench MP or a junior minister or even a cabinet minister, I'm certain that he would be for Leave," Hilton said in an interview with the Times.

Hilton added that Cameron is instinctively Eurosceptic. "That's who he is," said Hilton. "As prime minister he sees it from a different perspective, and that's perfectly reasonable ... but I think that if he didn't have that perspective he would be for Leave," he added.

The Conservative Party is divided over the EU referendum and Cameron has faced criticism over his handling of the issue, with a number of Tory MPs reportedly ready to trigger a vote of no confidence – no matter the outcome of the vote. Hilton's comments are likely to anger the government as it seeks to prevent a Brexit.

Earlier this month the former Number 10 adviser said EU membership "makes Britain literally ungovernable". In an article for the Daily Mail, Hilton claimed leaving the EU is about "taking back power from arrogant, unaccountable, hubristic elites and putting it where it belongs – in people's hands."

Back in 2013, Cameron announced that he would seek a "new settlement" for Britain's relationship with the EU during his Bloomberg speech. In February 2016, the prime minister unveiled a deal giving the UK "special status" in the EU, but Hilton said the reforms secured by Cameron are insufficient.

"I think that the demands were relatively modest and even those modest demands were treated with total contempt," he said.