The British election

I've become interested in the upcoming British elections, thanks to reading a post at America magazine by Matt Malone SJ, an American Jesuit living in the UK - Britain's Next Move and listening to a podcast interview with him here, plus seeing the news stories about the novelty of the first political debates ever in the UK. It's apparently because of these debates that the leader of the third and up to now less powerful political power, Nick Clegg of the Liberal Democrats, has become something of a dark horse. I don't know much at all about British politics and my main question is this - what's the ideological difference between the Labour Party and the Liberal Democrats?

Anyway, here's a YouTube of part of the debates ....