Lord Lawson poured a bucket of cold, Eurosceptic water over David Cameron's plan to earn key concessions from Brussels last night ahead of a referendum on the UK's membership of the EU.
The Tory peer and former Chancellor said the prime minister will probably only secure "inconsequential" changes and fail to deliver "fundamental change" for Britain.
But despite his scepticism over the prime minister's reform proposals, the Tory grandee predicted that the public will vote to stay within the 28-members bloc and then "regret" their decision.
"I think it's likely that the changes that Cameron will secure will be inconsequential, of no significance at all," Lawson told the BBC's Newsnight show.
"He will present them as a major change and I don't think there will be a two to one majority in favour – I don't think it will be as big as that – but given his authority, and the lack of a credible opposition leader, it will probably be the same result [as the 1975 referendum on the European Economic Community (EEC), when the UK voted to be part of the EU precursor]."
The comments come after Cameron went on a whistle stop tour of Europe to press his reform package in person. The prime minister travelled to France, Poland, the Netherlands and Germany, where he seemed to make some progress with Angela Merkel.
The German Chancellor gave Cameron a boost when she did failed to rule out a treaty change. But Ewa Kopacz, the Polish premier, dented the Conservative leader's campaign as she opposed his welfare reforms, which would bar EU citizens in the UK from taking in-work-benefits.
Andy Burnham, the favourite to win Labour's leadership race, has called for his party to set-up a separate "In" campaign.
The shadow health secretary wants Labour to make the move after the party worked alongside the Tories and the Liberal Democrats as part of the "Better Together" Scottish independence referendum campaign last year.
Meanwhile, the "Out" camp seems to be split over the issue as some Eurosceptics are holding back until Cameron has finished his negotiations and others are debating over who should lead their campaign.
John Mills, one of Labour's biggest donors, suggested that Kate Hoey should lead the "Out" group. Elsewhere, Ukip MEP Tim Aker argued that Nigel Farage should head up the campaign after his Eurosceptic party nearly secure four million votes at the general election.
But Douglas Carswell, Ukip's only MP, has suggested that a high-profile business leader like Eurosceptic and engineering entrepreneur James Dyson should lead the "Out" team.