Having sought various opinions and seen how other pilots have been treated, it seemed to me that there was a wide variation in how this rule/guideline is interpreted.
So I wrote to the CAA. I confirmed that this was the algorithm that should be followed-
http://www.caa.co.uk/docs/49/2008020...nAlgorithm.pdf
I then asked whether adherence to the above algorithm is compulsory for Class 1 medical holder pilots, or is at the discretion of the AME. The answer is unequivocal-
Adherence to the algorithm is compulsory for Class 1 certificate holders.
That would seem to sort it.