The decision by multi-millionaire Paul Sykes to pour "as much money as it takes" into Nigel Farage's Ukip may not be a huge surprise, but it will have deepened the gloom already hanging over the Tory party in the run-up to next year's EU elections.
The maverick businessman may have previously supported the Conservative Party, but he backed Ukip to the tune of £1.5m in 2004 and, with the Euro elections looming, it was always possible he would do so again.
It is easy for the Tories to write him off as a maverick, and he does have form on this front as one of the leading lights behind Sir James Goldsmith's campaign to "save the pound" in the 1990s.
That party made plenty of noise and caused some difficulties for the Tories but, ultimately, it faded away. Claims by Sykes that, had it not been for them, Britain would now be in the euro are, to say the least, exaggerated.
But, as he has proved in the past, Sykes does have the financial muscle and platform to cause the Tories problems as his numerous media interviews announcing his decision proved.
He has insisted his cash will be used "to give people a say about their future," adding: "We are going to roll some guns out. Every person in Britain will get to know a lot more from our campaign than they have ever got to know from all the other campaigns put together."
And that is where the danger lies. As the main political parties watch their spending in order to build up war chests for the 2015 general election, they will be facing a Euro election 12 months earlier with Ukip launching a well-financed, mass propaganda campaign.
What is worse, there is the real possibility for Cameron that some of his own MPs, and definitely many grassroots Tories, will find it difficult to be overly enthusiastic in their opposition to Ukip. Too many of them agree with the party's platform.
Come the general election, Cameron will be able to argue that only a vote for the Tories will guarantee an in-out referendum on the EU and that a vote for Ukip would risk letting in Labour.
Neither of those arguments will run in the European parliament elections next year. Ukip is already claiming it can win those elections and Sykes' campaigning cash will only make that more likely.
Such a victory will panic some in the Tory ranks, risk re-opening all the old rifts on the backbenches and provide a worrying backdrop for the 2015 campaign.
But membership of the EU never plays heavily in general elections so Cameron will hope he will be able to write it off as a protest vote and concentrate on the core message that a vote for Ukip would be a vote for Labour.