Referendum offer on voting gives Lib Dems late surprise

But in a last-ditch attempt to forge their own deal with the Liberal Democrats, the Tories offered a referendum on the Alternative Vote (AV) electoral system for Westminster elections.

Nick Clegg's Liberal Democrat party has a number of seats in the House of Common disproportionate to the votes it gathered in the election and wants proportional representation (PR) to replace the current First Past the Post system and give smaller parties wider representation in the House of Commons – a system which is widely used on the continent.

AV is a system in which a candidate has to receive more than 50 per cent of the vote to be elected. If no candidate receives more than half the votes, the second choices for the lowest ranked on the first count are redistributed. The process is repeated until one candidate gets an absolute majority.

The AV system however may not be enough for Mr Clegg's party, with Mr Brown offering a broader referendum on that would let people chose from a number of potential systems.

One option could be AV Plus – recommended by the Jenkins Commission in 1998 and but rejected by the then Labour Government.

AV Plus would see the majority of MPs elected using AV and the rest by a "top-up" system.

As well as voting for a constituency MP, each elector would get a second vote to cast at a county level or equivalent.

The Lib Dems prefer the Single Transferable Vote system, used in Scotland and Northern Ireland.