Stephen Sackur speaks to Douglas Carswell of the UK Independence Party. In early May the UK will hold what promises to be the most unpredictable general election in decades. As in much of Europe, voters appear alienated from the political establishment. The two main parties - Conservative and Labour - have both seen support drift away and neither appears capable of winning a majority. Frustration with politics as usual has fuelled the rise of Ukip, the populist, anti-EU party. How will Ukip withstand the intense scrutiny of an election campaign?