Basically, the Tories have been slipping in the polls, and so Gordon Brown has called for a May 6 election.
I think that it still an uphill battle, but the Tories appear to be in, “Stepping on their own dick,” mode right now, and one poll shows the margin to be only 4%, so it is an opportune time for Labour to call an election.
I think that it will be a close thing, but my record on such things is less than stellar.