Nigel Farage says David Cameron is a 'Eurofanatic'
Nigel Farage has accused David Cameron of winning elections by "pretending to be a Eurosceptic".
The UKIP leader said the PM was in fact a "Eurofanatic" who had been "deceiving the British people for years".
Accusations of lying have been levelled by both sides in recent days with the EU referendum debate becoming increasingly ill-tempered.
Mr Cameron said the EU was "not perfect" but that access to the single market justified the "frustrations".
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The UK's EU referendum takes place on 23 June.
Mr Farage, who has been touring the country in UKIP's purple bus, was asked about a recent row over Turkey's membership of the EU.
On Sunday Mr Cameron rebuked Armed Forces Minister Penny Mordaunt after she suggested the UK would not have a veto to prevent Turkey joining, saying she had made "a very misleading claim".
Mr Farage said Ms Mordaunt had made a mistake but claimed the PM would never be prepared to use a veto, because he had "campaigned" for Turkey to join for 10 years.
The UK government's formal position is to support Turkey joining the EU, but the PM said at the current rate of progress it would be the "year 3000" before this happened.
Mr Farage - who has also clashed with the official Leave campaign - is trying to contrast his street campaigning with the government's approach, BBC political correspondent Eleanor Garnier said.
The UKIP leader said the "whole apparatus of the state is being used" to persuade people to stay in, accusing Mr Cameron of "twisting and turning" on the EU.
The prime minister had gone from "ruling nothing out" during his negotiations to warning of "World War Three" if the UK leaves, he said.
"This man has won elections, and won votes, by pretending to be a Eurosceptic," he said.
"We are now seeing the real David Cameron. He's a Eurofanatic, he believes in the European project. He has been deceiving the British people for years."
Leave campaigners have reacted furiously to Treasury warnings about the economic consequences of a vote to leave, including on Monday that a recession could be triggered and on Tuesday that family holidays would get more expensive.
Speaking in Luton at Easyjet's headquarters, Mr Cameron said he had "great faith" that voters would back a Remain vote.
"Europe is not perfect, it can be frustrating," he said, adding that he thought it had improved following his renegotiations.
Despite the problems, he said it was in the UK's economic and security interests to remain in.