Many thanks for the helpful comments.
I absolutely agree that the recommendations are there for a reason, and we don't want to get poisoned. But the existing Poloma/flue has been fitted since the boat was built some 12 years ago, and it has gone through 3 BSS inspections without a mention of the flue position. (The most recent being 18 months ago). I expect that moving the flue would require another hole to be cut in the roof, and the existing hole covered over by some method.
I think I just got upset by the attitude of the guy who produced a BSS inspection check sheet dated 1999 (and thus well out of date) stating that the dimensions were mandatory and I had no choice.
As you quite rightly say, a different approach might have had a different result, but I did not get a warm feeling that the chap was not trying it on.
Thanks for the comments, much appreciated - and a great forum I have discovered. I will view it now with great interest.
Regards
Mike