The Labour Party are unlikely to call a general election whilst they are so far behind in the polls. Last month, the Tories lead Labour by 28%. There has since been a 'Brown Bounce' due to his handling of the financial crisis, but the Tory lead is still 12%. Not a time to call a snap election.
A more likely scenario is that Labour will ditch Brown if their popularity does not improve. As we have seen over the last month, a lot can happen in politics. Labour's rating has gone up 16% and the Tories have gone down 14%. A lot can happen to improve Labour's chances before June 2010. it is a bit premature to write them off now.