The information board at the published coordinates contains everything you need to work out final co-ordinates, it's a short walk to find the cache.
Final co-ordinates are N 54 42.XXX W 1 40.ZZZ
XXX is (((Hour of Wednesday Service x Last Digit of Phone number)+74) x Hour of Thursday Service) - ((Hour of Sunday Service x 4) + 4th character of postcode)
ZZZ is ((Hour of Sunday Service x Last Digit of Phone number) x 11) - Hour of Thursday Service.
Checkdigit=24