Just happened across this at cdkeys.com. I think it often drops this low, but couldn't see a recent deal on here with this price. Before anyone asks, note that this is a key for Origin - the game isn't available on Steam. I guess the 5% code makes it about £12.34 ish?
The Combat Runner DLC (which is just fluff for making you look different in other people's runs) is also available for 9p at the link below:http://www.cdkeys.com/pc/games/mirrors-edge-catalyst-combat-runner-kit-dlc-pc-origin