Thanks for your thoughts John, yes it's a company schedule for CAA approval. I've been working on it since I posted, and I think now that it's a case of slavish reproduction of the code without full understanding.
T'would appear that the old BCARs D and K, gave a rather vague reference to clamping two of the three primary controls and then doing a doublet on the other. I suspect that's probably something passed down through various revisions before finally being eliminated by JAR/FAR 25 & 23.
One does tend to see this on certification reports and schedules by people without a full understanding - a tendency to write schedules around the standard rather than the aeroplane. However, the incredibly vague wording re: handling in any of the civil standards is probably paying your and my mortages, so I shouldn't complain too loudly.
Happy new year to you as well.
G