Just spoken with the CAA.
EASA say and exam sitting is a period of 10 consecutive days. The CAA had originally said that it was one day.
They have now adjusted this - they now define a sitting as 3 consecutive days.
Not sure how this overcomes the fact that they are not allowed to change EASA's acceptable means of compliance (AMC) without getting a new AMC agreed but at least they're moving in the right direction...