http://www.caa.co.uk/docs/33/CAP804rfs.pdf
Doc linked to above looks relevant (takes some wading through). Call the CAA for the horses mouth.
Unless I've misunderstood the question, your friendly will have to apply for a new license (which will be an EASA non expiring license) and will have to revalidate his class ratings for both SEP and MEP.
I reval'd my PPL early last year. I was within the 7 year expiry period (just) so only had to pass a proficiency check to renew my SEP class rating (which expires after 2 years), and pay the CAA for a new license.
I missed the EASA cutoff so have been issued with another JAA license, which will be replaced by an EASA license next time I renew/add a rating.