I had a thought! Throughout industralised England, when waves of people want to move to London this forces an artificial boom of house prices to sell to the outsiders. When a new technology or generation comes along wanting to move to London, the same happens and this forces house Prices in London up.
Now, with the internet, it's possible to work for companies around the world without actually being present in that location. Group meetings, face-to-face meetings and instant communcation can happen without having to move to London. This is a boon for technological companies who don't have to pay as much for someone living elsewhere outside of London as they would situated in London.
So maybe, this has had a knock-on effect with a reduced amount of people wanting to move to London "because of work" which has prevented house prices from rising as dramatically as they would noramlly?