| 1843 | | Proposed | Drawing showing conjectural restoration of the National Monument. |
| 1949 | | Alteration/conversion | Development proposed for Festival of Britain celebrations |
| 1996 | 1997 | Proposed | £15-20million scheme for a large self supporting all-glass structure as a landmark millenium project. Works to include refurbishment of the existing observatory complex, provision of a visitor centre, landscaping and public transport.
The glass structure is designed to be interactive, with coloured laser displays to suit performances. |