MPs are to vote on whether to hold a referendum on scrapping Britain's first past the vote electoral system in favour of the Alternative Vote (AV). If AV had been used in previous general elections would it have changed the result?
This graphic illustrates how the results of the last six general elections might have looked had the 'alternative vote' system been in place. The overall outcome of the contests would not have changed, but the Liberal Democrats would have gained the most seats and the scale of the Conservative defeat in 1997 would have been much greater, the research suggests.
* The Lib Dems were formed in 1988 after contesting the 1983 and 1987 elections as the SDP-Alliance.
Note: This projection assumes that voters still select the same first choice candidate as they did in the first-past-the-post system.