How would you short London?

Here's a finance riddle: how would you short London's property bubble? House prices are up GBP50K in the last six months, our freeholder is making noises about either buying or forcing us out in order to build a giant tower, and they sold off Scotland Yard (!). They say the market can stay irrational longer than you can stay solvent, and I've been marvelling at the irrationality of London's property market since I moved there in 2003. Just for the sake of argument, if you wanted to put a bet down on a property value crash, how would you make it?