So closely guarded that it's the subject of both an AIC and a NOTAM.
AVW: Q)EGTT/QRTCA/IV/BO/W/000/030/5119N00207W002
FROM 06/05/27 08:00 TO 06/05/29 18:00 J1880/06
D)0800-1800
E)AUS 06-05-0004/1349/DAPLC
KEEVIL RESTRICTION OF FLYING REGULATIONS MADE UNDER ARTICLE 96 OF THE ANO 2005 (MIL ACFT SHOULD COMPLY WITH JSP552 201.135.9). NO ACFT SHALL FLY WI CIRCLE RADIUS 2NM CENTRED AT 511851N 0020637W EXCEPT ACFT FLYING WITH PPR AND CLEARANCE FROM ATC (130.675 MHZ) OR IN SERVICE OF OR WITH PERMISSION OF WILTSHIRE POLICE.
AIC 54/2006 (MAUVE 182) REFERS.
F)SFC G)3000FT AMSL