Writing in the new Political Studies Association magazine Political Insight leading electoral studies analyst Paul Whiteley uses a seats-vote model to forecast that Labour will be the largest party after the general election. He cautions, however, 'The data from 2005 suggest that the parties are so close together that either Conservatives or Labour could be the largest party in the House of Commons.'
He admits, 'There is one complication with the forecasting model, however: it is very difficult to model accurately the number of seats won by parties other than Labour, the Conservatives and the Liberal Democrats. This is because the seats won by minor parties are relatively unpredictable'.
I don't have a model to use, only my own intution and the opinion polls, but I would expect the Conservatives to be the largest party and have a small overall majority. But it's all still to play for.