At this point I usually put a plug in for the Ashbourne Fly-fishing club.
Nothing as sophisticated as a website, but plenty of great brook fishing, mainly wild trout and, as a bonus, some gems of largely-hidden unknown and unfished stillwaters, friendly if idiosyncratic members, and the waters are keepered
Costs about the same as DCAC, but a totally different experience.
Or, if you want to fish the mighty Derwent and 500 yards of the Wye there is also
Darley Dale Flyfishers
A bit more expensive also keepered.
However these places are a tad more than 2 hours from London.
PM me if interested in either of these