You should also consider Ofcom since they license them.
(A search of Ofcom for Debden came up with a map of band L radars in 2 mins. Also found a table listing numbers of radars by type in another 3 mins.)
A search of the CAA web site with Debden came up with the coordinates of all primary and secondary radars for Stansted, Heathrow & Gatwick so it's not a big secret.