Due to distances to existing caches in the area, I wasn't able to place it at the milestone, so the final cache is not located at the above co-ordinates. However, you will need to visit in order to collect two numbers written on the Milestone.
Distance to London = MS (it is just visible)
Please do not post spoiler pictures of the milepost in your logs! When you have signed, please roll the log up and put it back in the LID to make sure it's easy for the next cacher to remove.
You will also need to collect some information from the following Are We Nearly There Yet? caches:
AWNTY? Margaretting
AWNTY? White's Bridge
The final cache is a small micro at (beware muggles!):
N 51° Q(S-R).(R+P)(R+P)(N+P)
E 0° PS.(N+Q)(M+P)(S-N-P)