Last I know of, in addition to Buch, Boul, Neat and Holmpton:
Ash was bought by AL Digital as a Data Storage facility around 1994, "The Bunker", see:
www.thebunker.net
'Happidrome' building nearby is a Vet Surgery; this is the same design as Neat's R30 but that is more akin to the cancelled R9 design at Comberton where they to add rooms to one side for more control positions, the Tech offices were added following retention of the 'Happidrome' as a result of the 1966 fire - this building was scheduled for demolition the same year.
AL also have the Cruise Missile shelters and buildings at Greenham Common. Additionally, they showed interest in Bawdsey but that came to nothing.
Uncertain about most recently-vacated R3s. Of the rest (a total of 11 were built in UK):
R3 at Anstruther is another museum, see:
www.secretbunker.co.uk
R3 at Skendleby is another Data Storage facility since 2003, "Smartbunker", see website by typing lincolnshire smart bunker in address bar
This bunker had extra floors added by 1) removing the lower false floor and lowering the ceiling, which probably makes a restricted height for the middle floor; 2) building another level on top of the R3.
R3 at Sopley is still being used for document storage since being bought by a US company in 1993.
R3 at Seaton Snook is totally flooded, top of building exposed
R3 at Wartling is also flooded.
Funny how the R30 was designated to follow-on from the R3. Just like Saxa Vord - R101 followed R10.
Bunker in Essex is an R4 at Kelvedon Hatch. See:
www.secretnuclearbunker.com
There were 4 (3-floor) altogether, built as SOCs but not used as the R3s were quite capable of doing SOC and CRC at same time. Others are at Barnton Quarry (Edinburgh - vandalised), Bawburgh (Norwich - empty but site used for communications), Shipton (York - empty but intact with 4th floor added on top). 2 other SOCs at Longley Lane (Goosnargh, Lancashire) and Box (Wiltshire), both using WW2 buildings.
