Alf,
if you'd like to find out by yourself, where this given point is, you have to know at first, where Biddenden is located in the British Cassini Grid. According to:
http://www.echodelta.net/mbs/grilles...ishcassini.htm
it should be square wR.
If you then go to the page
http://www.echodelta.net/mbs/eng-translator.php
and type in wR294584 and click on "convert", you will get a rough map, that can be enlarged by clicking on the red cross.
By doing so, following map will appear:
http://www.mapquest.com/maps/map.adp....6515600092079
This map can be enlarged further.
Best wishes
Robert