Many thanks for all of your replies!
Where I work, practising the speechless code is a routine, even daily occurrence. A lesson I have learned from this particular scenario is it seems to be a dead art in the civil world. I'll certainly take the time to say "One click for yes, two for no" if I think it's a non military aircraft I'm talking to in future.
To address some of the other points made;
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Backpacker
1. I agree flying triangles is probably a waste of time, much better to squawk 7600 if you have a transponder.
2. This wasn't "an inexperienced and probably very stressed amateur" it was a well known name on the British display circuit who came accross as very arrogant on the phone.
3. If ATC does use two clicks for roger, then that's just them being gash!
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DFC
1. Yes I was.
2. I agree the pilot was right to provide feedback and it was welcomed.
3. You're wrong about No Compass No Giro procedures. The UK Mil phraseology is still "Adopt the no compass no giro procedure, making all turns rate one, starting and stopping on the executive word now." Speechless NCNG recoveries are a favourite practice emergency in my neck of the woods.
4. Click Click Click
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Thanks again to everyone who has contributed.
Stay Safe,
LXGB
PS - In case anyone missed the link in my first post,
you can download CAP413 here.