| Old Orchard Observatory | Fiddington | — |
| Olive Farm Observatory | South Ribble | — |
 Orwell Park observatory | Nacton | — |
| Penn Heights Observatory | Rickmansworth | — |
 Perrott's Folly | Birmingham | — |
| Peverell observatory | City of Plymouth | — |
| Portland Bird Observatory | — | — |
| Pymoor observatory | Downham | — |
| Quainton Observatory | Aylesbury | — |
| Ragdon Observatory | Church Stretton | — |
| Rayleigh Observatory | South Woodham Ferrers | 75 m |
 Real Observatorio de Edimburgo | City de Edimburgo | — |
 Real Observatorio de Greenwich | Municipio de Greenwich | 68 m |
 Reform Tower, Meethill, Invernettie | Aberdeenshire | — |
| Remains of Astronomical Observatory at Penllergaer | Swansea | — |
| Rolvenden observatory | Rolvenden | — |
| Romney Robinson Memorial Dome | Condado de Armagh | — |
| Rose Cottage Observatory | Keighley | — |
| Roseland Observatory | Cornwall | — |
| Runcorn observatory | Halton | — |
| Rushay Farm Observatory | Sturminster Newton | — |
| Sandwich Bay Bird Observatory | — | — |
 Scottish Dark Sky Observatory | East Ayrshire | — |
 Sherwood Observatory | Distrito de Ashfield | — |
| Skokholm Bird Observatory | — | — |
| South Meridian Marker | Ballyheridan | — |
| South Observatory | Waterlooville | — |
| South Wonston observatory | South Wonston | — |
| Southend Bradfield observatory | Bradfield | — |
| Southwater observatory | Southwater | — |
| Spaceguard Centre | Powys | — |
| Spurn Bird Observatory | — | — |
 St. Andrews observatory | Fife | — |
| Stakenbridge observatory | Kidderminster | — |
| Stanley Laver Observatory | Pontesbury | — |
 Stonyhurst Observatory | — | — |
| Stowupland observatory | Stowmarket | — |
| Strawberry Field observatory | City of Southampton | — |
| Sutton Bonington weather station | — | — |
| SWF observatory | Chelmsford | — |
| Swilken Brae observatory | Saint Andrews | — |
| Tarbatness Observatory | Highland | — |
| Telford observatory | Great Dawley | — |
 The Equatorial Observatory, Penllergare | Penllergaer | 79,7 m |
 The Observatory | Falmouth | — |
| The Studios Observatory | Grantham | — |
| Trent Astronomical Observatory | City of Nottingham | — |
| Tristan da Cunha Magnetic Observatory | — | 42 m |