Good on you OP.
Unfortunately there's not yet a system in place for self-exclusion across multiple operators, though the UKGC says there should be something by the end of the year, so might be worth keeping an eye on.
http://www.gamblingcommission.gov.uk...exclusion.aspx
As David says above, you can go through all licensed UK operators - this search result shows all Remote gaming licenses. There's a lot of them tho
https://secure.gamblingcommission.go...&Sector=Remote
Probably best is, as mentioned above, go to PokerScout and work down the list. Request that you are excluded network-wide on networks like MPN and iPoker.
Another avenue is perhaps block yourself at the payment processing level. Close any ewallets (skrill, neteller), call your credit card companies and ask them not to process any transactions coded as gambling.
It's probably best to get advice from the experts - they'll know the best practical steps forward.
http://www.gamcare.org.uk/