The referendum on Britain remaining in the European Union risks being a "David Cameron fix", Ukip's sole MP has said.
On BBC's Question Time in Gateshead, Douglas Carswell claimed the Prime Minister wanted to stay in the EU at "pretty much any price".
His comments come as legislation for the UK's first referendum since 1975 on staying in the union passed its fist hurdle in the House of Commons this week.
But the Prime Minister fuelled confusion by stating Cabinet minister's would not be allowed to have a free vote if they wanted to keep their jobs, only then to claim he had been "mis-interpreted" after a wave of front page headlines.
He said a decision would be made about ministerial collective responsibility after attempts to get a better settlement with EU leaders had concluded.
Mr Cameron was also criticised for abandoning the "purdah" principle, which would have limited state spending in the final weeks of the campaign.
Ukip's Mr Carswell, who defected from the Conservatives before the election, said this amounted to a "fix".
He told the audience: "It's now clear David Cameron wants to get an 'in' vote at pretty much any price.
"He's going to get his deal on Europe because he's not asking for much.
"It's also pretty clear he's trying to fix it by putting that pressure on his own Cabinet. He was forced to back down but only under duress.
"And also these rules of purdah. Having the civil service neutral in this campaign is absolutely vital. If you don't you've got this vast Government bureaucracy that is in fact a second branch of the 'in' campaign.
"I think it is absolutely vital if this is to be seen as free and fair, rather than a Cameron fix, then we need those rules of purdah."
Government minister Matt Hancock said the vote would be "free and fair", but opted then to attack Ukip over its "negative" outlook.
He cited a prominent businessman, whose family moved to the UK 60 years' ago, who now "feels unwelcome in this country ... because of the rhetoric of Ukip".
He added: "Even if there's just one person like that I think you need to take a long hard look in the mirror and think about the party you have joined."
But Mr Carswell responded: "I thought we were debating whether there should be a free and fair referendum? If you want to slur four million people who voted Ukip, go ahead."