You just go and be a contractor. There are tons of contracting positions open in London that will pay £500 - £600 per day. It's easy to make over £100k (pounds) if you're a good contractor.
A contractor (contract based, usually 3-6 month intervals, low paid) is a totally different thing to a freelancer (higher bill rate, hourly ad hoc projects usually) and a consultant (much higher bill rate, but project based instead fixed interval based).