Okey dokey, I'll assume no restrictions on it so, as it has lapsed by less than 5 years you can revalidate it with any JAA approved Aeromedical Examiner in any country and it is a simple revalidation examination.
If it had lapsed by more than 5 years and you have to go back to an Aeromedical Centre for an Extended Medical.
More than 10 years and it is back to the AMC for an Initial Medical again!!
HTH
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