Hi Mike and welcome.
According to EA fishery officers, the Thames has never been in better condition, fish climbing up the bank to be caught. Hmmmm, fat chance. However it's not as bleak (pardon the pun) as perhaps you make out. As Tinker says you have to get to know the stretches and at what times they fish best.
Are you in a club? Take at look at
our TVAA site (click on this). You can join one of the clubs listed, like Old Windsor AC say, on that site and fish any of the stretches listed there without further charge. Some are pretty good like Cliveden and I've had some decent little catches from Cookham. We did lose one big long stretch above Windsor, but hope to get it back eventually. Don't forget
free stretches too, like Marlow off Gossmore lane and Odney island in Cookham or Ray Mill Island in Maidenhead, they can produce some good catches.
What has happened over the years is the Thames is the favourite haunt of the beloved cormorant and fish have become very wary of it's presence and you have to fish in the early morning or late evening, night or under cover such as fallen trees, anywhere the dreaded black death can't get.
Good luck, for any more info send me a PM, I'll try and help.