By Jason Farrell, Senior Political Correspondent
A multi-millionaire businessman and long-term Conservative backer says he is switching his support to UKIP, Sky News can exclusively reveal.
On the day of David Cameron's conference speech, Arron Banks, who has previously made substantial contributions to the Tory party, said he had donated £1m to UKIP.
The donation was originally £100,000, but Mr Banks later said he had increased the amount after William Hague said he had never heard of him.
Mr Banks says he does not believe Mr Cameron will reform the EU and will not facilitate the UK's exit from it.
"I've supported the Conservatives for a number of years but have come to the realisation that only UKIP supports my views," he said.
He added: "Being a member of the EU is like having a first class ticket on the Titanic. Economically, remaining in the EU is unsustainable."
His switch comes a day after veteran Conservative MP Bill Cash learned his son William had decided to stand as a UKIP candidate and was also appointed the party's heritage spokesman.
It also follows the weekend defection of the Conservative MP for Rochester and Strood, Mark Reckless, who became the second Tory MP to force a by-election by changing sides.
There had been rumours of another defection on Wednesday as Tory delegates look to Mr Cameron to set out his policies to take his party into the next general election.
There will be some relief that it is not another name from the Commons, but also disappointment that Mr Farage's party is getting a financial boost.
It was an ex-Tory party donor, Paul Sykes, who funded a major advertising campaign for UKIP ahead of its successful May European Elections.
Another cash injection from a former Conservative benefactor is not just a transfer of funds, but also a psychological blow for a party that prides itself on having the support of business leaders.
Mr Banks was the founder of Brightside group, one of the largest insurance brokers in the UK.
He said: "The Conservative Party try to sell us the myth that EU reform is achievable when frankly all Cameron can offer is tinkering around the edges."
His donation is one of the largest ever given to UKIP and will help fund their three upcoming by-election campaigns.
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Gallery: Tory Party Conference: In Pictures
The Conservative Party Conference has drawn to a close. Here are some of the highlights: Boris Johnson addressed delegates with a brick - and cracked a joke about "purring" at David Cameron's expense ...
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But of course Boris and Dave are close - as they proved with this touching stroll together
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It was not Mr Cameron but Ed Miliband who was the butt of most jokes. The best one was the one about him forgetting to mention the deficit in his keynote address to the Labour Party Conference last week
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It shifted some merchandise such as this hilariously named beer
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George Osborne started it in his speech, during which he invited voters to choose Dave, choose the Conservatives and choose the future
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But it did make him sound like Renton from Trainspotting. Everyone thought so
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Nigel Farage was the spectre at the feast. Four defections to UKIP - one MP, a donor and two others since the conference began
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The PM prepared for his big speech by asking delegates what they thought of him by posting message boards around the conference in Birmingham
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And spent some time with Samantha, his wife
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He posed for selfies with delegates
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And did not miss a hard hat, high-vis opportunity
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He was photographed memorising the chapter on the deficit ... in glasses and Union flag cufflinks ...
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... as he prepared for the crowds in the main hall
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Where he gave some money away - tax cuts for the "hard-working"
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Got really cross about the NHS
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Then got clapped quite a lot
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Still, the Conservatives concluded that what Britain needs is an iron lady ...
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...and here's Home Secretary Theresa May
Labour frontbencher Michael Dugher said: "David Cameron is haemorrhaging support and his authority is ebbing away. He can't control his party, who clearly have no confidence in his leadership."
Speaking to Sky News Leader of the House of Commons William Hague said UKIP lacked the "strength and depth" to be a reasonable proposition to lead the contry.
He said: "UKIP is entirely a one-man band."