Itd be an electoral reform. I dont think labour (red) or the conservatives (blue) are particularly keen on it as the current system benefits them, although obviously they dont shout about it as everyones pledging to 'clean up politics.'
My history is pretty weak, but as i understand it the conservatives and liberal democrats (or more accurately, the roughly equivalent party) where the major parties before the 19th century, so they did used to be more powerful, but in the last 75 years or so theyve not been a major player.