Hi Rod1,
NATS is refitting all its radars to Mode "S". Currently I can think of the Debden and the Pease, I am not sure if the Clee is mode S but i am sure someone can enlighten us. But with the two that I mentioned, most of the London FIR is covered by Mode S.
I think NATS also has a feed of mode S in the west country area, but I can't remember from where
