Agreed, that's way too high for London. London does pay more compared to the rest of the UK but a typical web developer with 3yrs experience does not get £90k for working in London. I've seen under half that for cool startups and never above 2/3rds that for someone with only 3 years experience.
But then a contractor can earn much more. The low end is £350 per day up to around £650 per day.