Nate Silver's current projection of the election result:
If seats in the House of Commons are distributed exactly as our model suggests, it would create an unusual situation in which Conservatives alone could not form a majority, but Labour and Liberal Democrats could also not combine to form a majority. My personal view is that the most likely outcome of such a scenario would be a Conservative minority government, possibly followed by new elections in relatively short order as Conservatives sought to win an outright majority.
The Tory nightmare scenario - foretold to me last autumn by a senior Tory - is that they have to govern as a minority government, enact stringent spending cuts and then face an angry electorate after a few months, because their minority government is brought down in the Commons. In other words: the Tories would be used to do the dirty work of actually cutting spending and then pilloried and replaced.
Renard Sexton crunches the numbers various ways. An unlikely but frightening scenario:
Labour could pull off a 13 seat plurality of seats, while sneaking in third place in the national popular vote.