Stapleford is not in Kent of course; and the D.O.C. of an air to ground frequency is usually limited to a maximum of 10 miles from the station. This means that pilots should not be trying to transmit on the frequency outside this range. By doing so they may be causing all sorts of problems for other units that have been also been allocated the frequency (in different geographical areas) perhaps amongst them Brest Control!
Interesting point. And AFAIR there's a maximum altitude for certain ground stations too -- is it 3000 ft for tower/AFIS/AG? (Where is DOC listed, BTW? I can't find anything in the AIP or CAP413.)
So given that places like Sibson drop parachutists from up to FL150, how am I supposed to ask them what their activity status is when I'm flying close by at FL90?