General Election - October 2010 or May 2011?

So now we have a second poll, this time from BPIX for the Mail on Sunday that puts the Lib Dems in the lead and Cleggmania is rolling.

This could soon become very interesting, because, if it's sustainable (still questionable). and the Lib Dems came first in the popular vote, they would probably still end up only the third largest party in the Commons. If that happened then PR will be inevitable, after all, none of the other parties could win the argument that the system produces an equitable outcome.

When the Lib Dems have polls below 20%, Labour and the Tories can get away with ignoring the argument. However, if the results of today's opinion polls were mirrored across the country it would be impossible to ignore it any more.

So, let;s play a game for a second, imagine the Lib Dems won the popular vote but were the third largest party. Would we perhaps see a very short Parliament that produced just one law change, the introduction of proper PR along the lines of the Single Transferable Vote, and then a quick dissolution and General Election under the new system?

Could a full term Parliament be maintained before going down the PR route or would it not have to the case that the system is changed, and another vote is held? I wonder what odds the bookies would give on another General Election under a new voting system within 12 months of May 6th?