I know you have stipulated Cambridgeshire area but is Norfolk out of the question, even Suffolk?
I don't know much about Taverham Mills any more, fish wise, but I did breakdown almost every swim on there in a post on here. You paid your money, chose your swim, no swim booking and could move if need be.
The other option I was thinking of is Suffolk Water Park Traditional lake. You may have to book an individual swim, I am not sure, but there are definitely some good fish in there.
I hate being stuck in one swim, if the fish aren't there I do want to be able to move onto them