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The Brexit campaign was exposed as a con today as another chief cheerleader backed away from claims leaving the EU would mean an extra £350million a week for the NHS.

Former Work and Pensions Secretary Iain Duncan Smith joined Nigel Farage in distancing himself from the key referendum vow – as Brexiteers warned voters not to expect a quick drop in immigration following the historic poll result.

And a Tory MP who is expected to back Boris Johnson for the party leadership even admitted Vote Leave had “no plan” in place for dealing with Brexit .

Brexiteers had indicated the £350million – the gross cash sent by the UK to Brussels each week before a rebate and grants – could be ploughed into the ailing NHS .

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But Mr Duncan Smith said: “It is not a promise broken, I never said that through the course of the election.

"What I said was we will be able to spend the lion’s share of that.

"We said we’d stand by some critical areas, those areas that are being funded, structural regional funds will be funded.

“We’d have more money to spend on the NHS because we wouldn’t be losing half of that sum of money and we’d stand by commitments that have been made to things like agriculture.

"The rest were just a series of possibilities of what you could then do beyond those main commitments.”

(Image: REUTERS/Darren Staples)

The disputed £350million figure formed a key plank of Vote Leave’s campaign and its battle bus was emblazoned with the words: “We send the EU £350million a week – let’s fund our NHS instead.”

But just hours after Vote Leave’s victory was confirmed on Friday, UKIP leader Mr Farage said: “I can’t and I would never have made that claim – it was one of the mistakes that the Leave campaign made.”

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UKIP’s leader in Wales, Nathan Gill, also signalled the cash would not be available for the NHS, saying: “I never made that promise. I don’t know anything about it.”

Leave supporters are also reeling from admissions there will be no immediate drop in immigration.

Many voted for Brexit on the back of Vote Leave’s claim they could slash net migration. Yet Tory campaigner Steve Baker warned the Mirror not to expect a sudden plunge in the net 333,000 coming here every year.

(Image: REUTERS/Stefan Wermuth)

He said: “Until we have changed the law so we can conduct migration policy on the basis of British citizenship, we won’t be able to bring it down.

"What is needed is a statement explaining what will happen, and from that statement, dates. But there is a point after which migration policy will be conducted on the basis of citizenship.”

The chaos triggered by Brexit was outlined by a Conservative MP who told Sky News that Downing Street should have drawn up a blueprint for life post-Brexit – even though the Government and PM backed Remain.

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The MP reportedly said: “There is no plan, Leave don’t have a post- Brexit plan. No 10 should have had a plan.”

And Tory big beast Lord Heseltine said: “We have a great gaping hole in Britain’s future.

"We have heard endlessly from Brexit leaders about the restoration of national sovereignty but not a word about how that sovereignty would be exercised prior to approval of the new Brexit arrangements.

"It is one thing to jump into a gaping hole but jumping is the easy bit: you are still left inside a gaping hole.”

(Image: Getty Images)

Divisions emerged in Europe over the speed and terms of the UK’s departure.

German Chancellor Angela Merkel suggested there should be no rush and her chief of staff, Peter Altmaier, said Westminster should have time to think through the consequences of Brexit.

But German Foreign Minister Frank-Walter Steinmeier said: “This process should get under way as soon as possible so we can concentrate on the future of Europe.”

And French Foreign Minister Jean-Marc Ayrault added: “We have to give a new sense to Europe, otherwise populism will fill the gap.”

US Secretary of State John Kerry will fly to Brussels and London today to discuss the implications of Brexit with leading EU leaders and Foreign ­Secretary Philip Hammond .

A senior US official said he would also stress the importance of other members not following Britain’s lead.

The formal process of Brexit will start when Westminster triggers Article 50 of the Lisbon Treaty, from which point he UK has two years.

In his resignation speech, David Cameron , who previously said he would invoke Article 50 immediately, said that would fall to his successor.