The first set of coordinates take you to a small parking place on a
quiet side road. Close by you will see a large yellow and black
circular sign.
The distance to London gives you a, b and c of the final
cache coordinates.
Take the first digit and multiply it by 7 to get a,
multiply the second by 6 to get b, and add the 3rd digit to
the number of miles to the next village, which is also shown on the
disc, to get c
Taking note of the advice on the sign, set off to the final
location which is not very far away. However, whether you go by car
or on foot, you will have to cross a busy road.
The final cache coordinates are 51°N 36.abc 002°W
26.748
The cache contains some coins and a logbook and you will need to
take a pencil.
If you find another of these yellow and black discs anywhere in
Britain you can log them on Waymarking.com.
You can find out more about waymarking
here
Once you have logged in go to Directory, Things, Signs
and look for Automobile Association Signs.
There are photos of disks here.
If you scroll to the bottom of the page you have opened you will
find an excellent list of all known sites. If you find one of the
disks be sure to log it on Waymarking.com
Good hunting.