Yes Paul, i also fish the Derwent in fact i had a great couple of sessions a few weeks ago targeting Grayling, i had 15 on the Saturday and a further 11 Grayling on the Sunday i was with a client on a guiding day, he took 6 Grayling and 4 Trout the best going 1.5lb and they generally averaged about 10oz.
As for the Fly fishing i like Carsington best Phil Straton the manager is a sound chap and has put some good fish in over the last two years and now they are really starting to grow on its well worth a visit, Foremark is another well run venue, the fish are there but soon wise up due to the catch and release system, so scale down with the fly size.
I would be happy to book you a days guiding and would include a free casting lesson e-mail me if you want to discuss it further mate and that goes for anyone else that fancys a days tuition.