You do need a JAA examiner to sign-off a renewal before expiry.
When you get back to Blighty you can revalidate by doing a skill test with an examiner (within 5 years). This is basicaly the same as the original skill test, but the examiner has some discretion to be selective. The navigation element is often minimal, for example, but you need to be prepared to do the whole thing if the examiner wants it.
Have you got the required one hour flight with an instructor signed off as well? If not, the cost of the test will not be too much more than that would have been.