Norton,
I would ask the CAA this one directly but I would think the following would be the position.
When you fill in the form for your renewal (answering the same questions as for your initial) you tick the appropriate box 'Yes' and in the comments section you put the question number and 'Previously Declared - No Change' or words to that effect. That should be enough for the AME who will know that the form is going off to the CAA Aero Medical Section and if there is anything incorrect on the form it will be picked up by the AMS staff and the medical revoked by them.
It isn't for the AME to police the situation although he/she may wish to clarify the position with the CAA first - make sure you go for your renewal during working hours so he can phone the AMS.
HTH
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