Chris J Dixon wrote:


Access is only from above. The screw is in a recess, and close to
a raised surround, making it pretty tricky to get at. Removing
one of the ordinary screws in the symmetrical location reveals it
to be a self tapper about 20 mm long.


How about a diamond tipped screwdriver blade? Apply a lot of pressure and
who knows, you might get lucky.

http://www.screwfix.com/p/wera-bitor...5-6-25mm/86103

Not too expensive either.

Tim