Some months ago I contacted the CAA - medical division on a similar issue, here's their answer:
"The Joint Aviation Requirements state that if you allow your JAR Class 1 medical to expire for less than 2 years from the date of expiry, you can go to an Approved Medical Examiner to renew your medical.
If you allow your medical to expire for more than 2 years, but less than 5
years your Approved Medical Examiner would have to gain permission from us
before proceeding with the medical. If you allow you medical certificate to
expire for more than 5 years from the date of expiry, you would have to
attend our AMC in Gatwick for an initial UK JAR Class 1 medical."
As for the eye form, here's the link:
http://www.caa.co.uk/docs/49/SRG_MED...structions.pdf
Cheers!!
