There is an excellent piece of research on Political Betting this morning by David Herdson which details how there is a loophole that would allow Gordon Brown to potentially stay on as Prime Minister until 2013!
I'll let David explain it:
The assumption has always been that once parliament expires, writs will be issued for the general election, which according to the timetable currently in force would put the date of the election on Thursday June 3 (or possibly Friday June 4 if the writs were issued the day after expiry - though that would break with the tradition of elections being on a Thursday).However, parliament has not expired in modern times; a dissolution has always been the mechanism through which a general election has been called. That, however, does not mean that a dissolution has to take place.The only statutory requirement to move writs for a general election is under the Meeting of Parliament Act 1694, which allows no less than three years between the dissolution and the writs being issued. In other words, technically, the election doesn’t have to be held until June 2013.
David then goes on to explain how realistically Brown would never get away with extending the parliament for so long, not least because all sorts of laws would lapse as they could not be renewed including the budget. He does however think that a delay of a few weeks or a even a few months could happen if a pretext could be found.
I think it is very unlikely, but I have been quite interested to see some of the responses to David's in the comments below his post. A number of people think that the Queen would step in to stop this but I think they are wrong. If an extension was to happen you can bet your bottom dollar that all the government's muscle would be put behind it. Whatever the mooted reason (Swine flu, Economy, National security etc.) would be hammered at on the media day after day and the cries of foul play would be spun as being against the national interest or some-such. It would become an intensely political situation and the idea that the Queen would step in to resolve it is in my opinion fantasy-land irrespective of whether she technically could. She is not going to want to provoke a constitutional crisis that could lead to the fall of the monarchy (and make no mistake, acting against the Prime Minister could precipitate that).
Anyway, this is probably all pie in the sky. I don't think the government would try this on and if they did, in the eventual General Election they would be utterly slaughtered and deservedly so. It's an interesting academic point though for political geeks like me.