What decides who becomes prime minister after the general election? No, it’s not voters. It’s this document: the Cabinet Manual.

The Manual is one of most important bits of our constitution. It covers all sorts of issues around the formation and conduct of government. That includes what happens in the event of a hung parliament like the one most people expect this week.

And if that happens, the following paragraph could just become the subject of an almighty political row that will decide who ends up governing.

2.12

Where an election does not result in an overall majority for a single party, the incumbent government remains in office unless and until the Prime Minister tenders his or her resignation and the Government’s resignation to the Sovereign. An incumbent government is entitled to wait until the new Parliament has met to see if it can command the confidence of the House of Commons, but is expected to resign if it becomes clear that it is unlikely to be able to command that confidence and there is a clear alternative.

In two sentences, that paragraph does lots of things, things that could be very, very important after the election.

The first sentence makes clear that unless Labour wins a clear majority, David Cameron gets to stay in Downing Street for a little while longer. In 2010 when Gordon Brown remained as PM after the election, Tories talked about him “squatting” in defiance of the electorate. In fact, he was acting quite properly, just as Mr Cameron will be by staying in No 10 on Friday morning.

That much is clear and largely accepted by all sides. It’s the second sentence where things could get heated.

Let’s suppose that the election numbers work out something like this: CON: 285 LD: 25 LAB: 265 SNP: 50 DUP: 8 UKIP: 2 OTHER 15

That could allow Mr Cameron to piece together a Conservative/Lib Dem/DUP/Ukip deal that would have 320 votes: not enough for a majority, but potentially enough to argue that he should stay in office to put a Queen’s Speech to the Commons, then dare Labour and the SNP to try to muster the votes to reject it then defeat him in a confidence vote. He’d doubtless argue that it would be unacceptable for a second-placed Labour Party to seek to oust the party that won the most seats and votes; I expect the phrase “coalition of losers” would figure in his arguments.

David Fuller's view

There is a lot to play for in the last two days but if the number of seats held by different parties resembles what we see above, the UK is in for a very unsettled post-election period.  Currently, odds shown by Betfair in the second half of the article above show Conservatives gaining the most seats but well short of an overall majority.  Betfair also shows Labour having the best odds of forming a government, despite trailing the Conservatives in seats likely to be held.  This is because the Scottish Nationalists, who want to leave the UK, have said they will support a minority Labour government to keep the Conservatives out.     

My guess is that Conservatives will receive the most votes and more seats that the 285 figure shown above.  However, the probability is that they still fall short of the 326 seats required for an overall majority, mainly because Liberal Democrats in the current coalition government voted with Labour in 2013 to block a redrawing of Commons boundaries to reflect population shifts.  Consequently, Conservative votes are diluted because many more people live in their constituencies, rather than Labour’s.