Help to identify unusual morse key
 

Hi, I wonder if any morse key collectors
out there can help identify this key
http://www.atdi24.dsl.pipex.com/mystery_key.htm
Most of it looks original except for a piece of
ali across the bridge, it has reference numbers
which don't seem to relate to anything
AM Ref No 10F / 8782 P.S.4707G No 142581
It points to an Air Ministry key but I've found
nothing similar..
Its a fine key, with a very nice action.
recent ebay purchase :)

from Ron..