You have a number of options nearer to where you are than the suggestions so far.
This site suggests places in Norfolk
http://www.fishandfly.co.uk/norfolk.html
I believe that there is some trout fishing on the upper Cam, but don't have any details. There's also whispers about the Chelmer
Moving west, in Herts there a number of small chalkstreams, however most have very restricted access on a day ticket. I fish a stretch of the Chess on the Bucks / Herts border but theres no day ticket I'm afraid.
The only bit I know in this area is a small stretch of the Ver that's available here.
http://redbournburyfishery.co.uk/default.aspx
The upper Ouse in West Suffolk has trout and sea trout but don't know about access, there's also fishing on the River Arun I think. Google these and day ticket and you should find something.
Alternatively yes you can fish the Blackwater estuary for bass. I sometimes fish the Crouch, if you're intersted PM and I could point you in the right direction possibly.
Good luck
John