My last non-banking contract rate was 750/day in London. It depends a lot based on whether or not you have experience from any "hot" niches, and also depends greatly on whether or not you develop relationships direct with clients or go via an agency.

E.g. direct with clients it's perfectly possible to get contracts at 1k/day+ in London for relatively normal development jobs outside of banking once you have relationships with the right companies and you approach them as a consultancy rather than presenting yourself as an individual developer.