UKIP’s Eastern region chairman declared at their conference in Doncaster that if half of its Westminster seats at the next election were not in his region he would go.

Victory for Douglas Carswell as the UKIP candidate for Clacton put the party on its way to achieving that.

There has been plenty of talk about the prospects for the East, and with its three Euro MPs, its ever-growing band of councillors and favourable polls – a Westminster seat would be the next stop on its staggering march.

But the big question on everyone’s lips will be whether the party can hold, double, triple even quadruple its House of Commons presence when the whole country is going to the polls and the party is fighting a war on many fronts.

UKIP is building a significant local base. The huge turnout at its public meetings is proof that it can mobilise grassroots support. But in many ways it is still an unknown. UKIP councillors need to prove they are effective at local council, and indeed European level, and convince their supporters they can do the same in Westminster.

Like the Liberal Democrats, they will discover it is easy to make populist promises, but being in power amid huge budget cuts is a very different matter.

And do they have the resources for the fight? They claim so.

But while UKIP has taken a seat from the Conservatives, Carswell’s victory should be equally concerning for the Labour Party. Mr Carswell took his old Harwich constituency from Labour in 2005.

And elsewhere in the East of England, UKIP threaten in places like Thurrock, Waveney and Great Yarmouth – key targets if Ed Miliband is to claim the keys to No.10.

So often both the Conservatives and Labour dismiss the threat of UKIP, suggesting that when it comes to Westminster seats their supporters will come flooding back. But with victory for Douglas Carswell, that argument quickly loses traction.