Why is UKIP so bitterly divided?

With an EU referendum coming up in June 2016, it would be expected that UKIP would be seizing the moment.

But despite winning four million votes in the General Election, and the Conservative and Labour parties battling with their own divisions, UKIP has fallen victim to infighting itself.

So why is Nigel Farage's party so bitterly divided?

Giles Dilnot reports