There is nothing at the published coordinates.
The bonus cache for a mini series of caches in and around the red phone boxes of Cam. These have been adopted by the local council and looked after by volunteers so that the iconic boxes can stay as points of interest for the community even though the phones are no longer operational.
To find this cache you will need to obtain information from the other caches in the series:
A: GC82TAH - Draycott
B: GC840DB - Cam Green Park
C: GC840DE - Cam Green / Ashmead
Then you need to visit N51° 41.496, W002° 21.090 (virtual stage 01) to find the final piece of required information:
Cabinet No = DEFG
And then use the information in the following formula to find the final cache container, which is a short walk away at:
N51 41. A B 7, W002 2C. (D-F) D F.
More information on the red phone boxes of Cam can be found at: https://www.camparishcouncil.gov.uk/bt-red-telephone-boxes-project.html