I'm now given to replying to my own threads to make myself look popular
Check out:
http://www.caa.co.uk/srg/med/default.asp?page=779#dev
This is the interesting bit (which appears to have been adopted) in case you can't be bothered:
Thus a small number of pilots, who might fall just outside the JAR medical requirements, but who the UK CAA feel are fit, either through specialised medical opinion or through demonstrated ability, could receive JAR medical certificates. These would be limited to flying on aircraft of the state of licence issue unless another state agreed to mutually recognise the Deviation. The possibility of using a Deviation on a medical certificate will be discussed further within the JAA.
The interesting thing is, if you're 'out' for the initial but 'in' for the renewal, does the deviation get lifted?