What if the voters don't choose anyone?

Polls slipping for Cameron, Gordon Brown vows to go on and on, Lib Dems getting equal footing in the TV debates - are we in hung parliament territory?

I took part in a Radio nan Gaidheal debate this morning on the subject just as Peter Hennessey,Professor of Contemporary British History, was on the posh radio - Radio 4 - on the same subject.

I suspect you'll find his summary of what might happen in the event of a hung parliament more enlightening if no more straightforward.

Hennessey was one of the people who recently helped Cabinet Secretary Gus O’Donnell translate put the tacit understandings of custom, practice and precedent into a draft cabinet manual on the formation of a government.

Hennessey described the exercise as "moving the constitution from the back of an envelope to the back of code".

So, Prof, what happens if the Conservatives are just ahead in the number of seats but don't have enough for a majority?

Theoretically, and practically knowing Gordon Brown, the Prime Minister can where he or she is, in 10 Downing Street. According to Prof H the PM of the day does not activate the Queen until he resigns.

Before that happens he could face parliament and only when voted down on a Queen’s Speech, a motion of confidence, would he have to resign. So plenty of time to wrangle a coalition deal if the news monster and the markets have the patience for it.

Gordon Brown has, of course, the option of asking for another dissolution if he loses a vote of confidence, but the Queen does not have to grant that request. It would be reckoned that he had his turn.

Then the Queen turns to the political figure who commands most seats or is most likely to command the confidence of the House of Commons - that would be David Cameron.

She offers the chance to David Cameron to form a government. If he loses a confidence vote, he can trigger a dissolution - another general election - and that would be granted.

Gordon Brown, at this stage, could still be leader of the Labour Party and go into another election facing Cameron. He said today he wanted to carry on and get a majority.

Hennessey reckons the parties would have to sort out most of the post-election mess themselves and that the Queen would just "give her good housekeeping seal of approval".

Then there would be all the back door negotiations with the minority parties to try and make a deal to stay in office.

Brown tried to lash up a deal with the Lib Dems in Scotland the weekend after Jack McConnell ended up with one seat less than Alex Salmond in the last Scottish election.

He wasn't successful at all that time but these Lib Dems with the most experience of negotiating deals - Jim Wallace, now Lord Wallace and Menzies Campbell who was sounded out in 2007 - will be the men to watch if it is a hung parliament. The SNP and Plaid have their shopping list, the Ulster Unionists their alliance with the Tories.

The door of Downing Street could be busy and watch out also for sales of wood varnish around Westminster. If it's a hung parliament they're going to be dragging Gordon out by the worn down quick of his fingernails.