Google earth maybe, Or do a cross reference OS grid reference cross thing.
http://www.google.com/search?hl=en&q=OS+grid+reference+converter&btnG=Search
Or just put the numbers into your GPS, Or your friends GPS.
http://www.google.com/search?hl=en&q=OS+grid+reference+converter&btnG=Search
Or just put the numbers into your GPS, Or your friends GPS.