If you have UK CAA licence is it National or JAA? either way something must have expired or you would already have an EASA licence.
If ratings have expired you will need course completion certificate for a renewal before you can test.
As its a UK Licence, non UK Examiners may be able to test, but most probably can't sign you up as they can only sign licences issued by the State that issues their certificate.
Probably best to renew/revalidate and convert in UK, then if you wish change your State of Licence Issue, bearing in mind that if you don't live there or work for a company there, they may not want to play.