Contracting rates, at £400 - £600 / day are more in line with the living costs.
But it's quite sad to see that living and property costs in London have become so insane that even senior software developers either have to contract or end up earning just about enough to pay the rent but not much more.
On the other side, a good seed round for an early stage startup in London is £200k. Maybe £300k if you're the hottest startup in town and work incredibly hard on your round. You're not going to be able to pay your employees very much at all with so little funding.
To me, the numbers just don't add up. I don't see how London can build a sustainable startup community. Or even tech community to be honest.