Being the biggest party but falling short of a majority might not get Ed Miliband into Downing Street. The Mail today suggests that the Lib Dems might pair up with the Tories in such a situation:

Senior Liberal Democrats are plotting a second coalition with the Conservatives even if Labour wins more Commons seats in next year’s general election…Another senior MP said there was a strong possibility that the Tories could gain more votes than Labour, but fewer seats, while Ukip could gain more votes than the Lib Dems, but no seats.While a Lib-Lab coalition would be possible in those circumstances, it would lack ‘democratic legitimacy’ in the eyes of many people, the MP said.

Which is pretty much what I said would be the case back in February:

“Lib Dem overtures and talk of government should be ignored for a more simple reason. Basic maths.

A coalition between Labour and the Lib Dems is incredibly unlikely to come to pass, both electorally and politically.

Let us consider the realities of our electoral system.

If Labour has a poll lead – Labour will have a majority and no need for a Lib Dem crutch.

If Labour and the Tories are tied on voteshare – As one strategist said to me a few months ago “we still win”. It’d be an ugly win, sure, but there’s be a commons majority and no need for the Lib Dems.

If the Tories win the popular vote but don’t get a majority – The only way in which a Labour/Lib Dem coalition can come to pass is if Labour is the largest party but doesn’t have a majority (or has such a small majority that governing is impossible). The only way that can happen is if Labour gets less of the popular vote than the Tories. As explained above – a draw or a win for Labour delivers a majority. It’s frankly unfeasible – and would require a change of heart quite spectacular even by Lib Dem standards – that the party who believe in Proportional Representation would back Labour if we’d come second in the election. And from Labour’s point of view it’d be toxic too – a “coalition of the losers” ruling the roost after a Westminster stitch up.”

Labour needs to get a majority in May 2015 – anything less, and there’s still a very good chance that the Lib Dems will send Cameron back to Downing Street. Again..