Douglas Carswell presents an existential threat - not just to the Tory party, but also to Ukip itself.

His victory speech after winning the Clacton by-election last night was a leadership speech in all but name. And not just any leader's speech. It was a direct challenge to Nigel Farage's political values.

It's worth quoting at length:

The speech echoes Carswell's first comments as he defected to Ukip in August, when he spoke up for political correctness and diversity. They were literally the first words out his mouth.

Compare these statements with Farage's outburst about barring entry to Britain for people who are HIV positive.

Talking to Newsweek Europe last night he was asked who should be allowed to enter Britain. "People who do not have HIV, to be frank," he answered. "That's a good start. And people with a skill." Remarkably he chose to defend those comments this morning, rather than retract them.

Carswell was always going to be a problem for Farage. Ukip has been a one-man show for a long time. A concerted effort has gone into diversifying its public face, but what Nigel says still goes. When it turned out Ukip already had a Clacton candidate, I asked one Ukip expert what the party's system was for dealing with the situation. "Whatever Nigel says," he replied. When you speak to Ukip members, they talk about Farage like some sort of beer-drinking messiah. It’s an almost Peronista level of domination by a charismatic figurehead.

Ukip is now slowly going to turn into a two-headed beast. Carswell is one of the very few politicians in Britain who has the personal brand, the media attention and the intellectual framework to challenge Farage. And, crucially, his politics are a million miles away.

This morning, as he tours news studios celebrating his victory, he will be asked about those Farage HIV comments. It is a precursor to a process we will see repeated many times over the years to come. Carswell is right wing and eurosceptic. But he holds completely different values to Farage. Farage is a Daily Express editorial from the 1980s, injected with blood and sparked into life by terrifying forces of political darkness. He is Thatcher with a striped suit and a drinking habit.

Carswell is quite different. He accepts the social victory of the left since the 1980s. He supports multiculturalism and knows politicians must accept the changing face of Britain if they are to win power. He is instinctively libertarian, whereas Farage is a knee-jerk authoritarian. The difference between the two men is not abstract or vague, it is foundational: Carswell likes modern Britain, Farage doesn't. That emotional thrust is pivotal to how Ukip defines itself and who it appeals to.

For now, the two men share the same enemy. They both want to shake up Westminster. But for Farage, it’s a fight against London-centric, diverse, cosmopolitan Britain, a glossy moisturiser looking out of place on a village green. For Carswell, Ukip is a chance to smash the fossilised Westminster two-party system, where independent thinkers are frozen out the circles of power.

Ukip is surging right now and quite probably the prospect of causing a significant upset in May 2015 will keep it relatively united until then. But the party is already riven with the same conflict of personalities and principles which tear apart Tories, Liberal Democrats and Labour. Soon enough, the fundamental incompatibility of Carswell and Farage will bubble up violently to the surface.