In the (currently missing) Doomwatch Series 3 episode "Flood" (TX.31/7/72), Dr. Tadley of Birdsnest does indeed roll up at the Doomwatch office to aid the team. Tadley is based in Aldermaston; the late Dr. Thirlaway was head of the Atomic Weapons Establishment's Blacknest unit based in the Berkshire village during the episode's production, perhaps helping author Ian Curteis with his scientific research.
Although Derek Benfield's character is down as Tadley in the surviving rehearsal script, reference works seem to credit him as Ridley. As the obit seems to infer it was the Tadley name which went to air, it is possible that the relevant Radio Times issue (from which future cast lists would be largely compiled) maybe mis-spelled it - or perhaps the name was changed for transmission. If anyone has the issue of the Radio Times detailing "Flood", please get in touch with this site.
Thanks to Tony Darbyshire for spotting this news item and to The Times Online.