The CAA will probably ask you whether you've read LASORS.....
G5.1 LICENCE RE-ISSUE
For a licence to be valid, a pilot must hold a current
medical certificate appropriate to the licence held, and
have a valid aircraft rating. Applicants may apply for the
re-issue of a licence within a period of 60 days prior to
the expiry date of the licence.
Holders of a lifetime UK PPL should note that the
licence itself is un-expiring, but the privileges conferred
by it, and by any ratings in it, may only be exercised
when the licence and the appropriate ratings are valid.
Re-validation or renewal of the appropriate rating(s) is
specified in Section F. Details to revalidate or renew a
FRTOL (if held) are specified in Section B.
A UK National or JAR-FCL Pilot’s Licence will be
re-issued for a further period (5 or 10 year validity as
appropriate to the licence held) subject to meeting the
following:-
1. hold a medical certificate appropriate to the licence
being re-issued valid for the first day of issue of the
new licence.
2. have held a valid Certificate of Test, Certificate of
Experience or Certificate of Revalidation for any
type/class rating that has not expired by more than
5 years*.
*Applicants who are currently flying under the privileges
of a non-UK ICAO licence and are currently flying an
aircraft type endorsed within their UK or JAR-FCL
licence, may have their licence re-issued by holding a
valid medical certificate appropriate to the licence being
re-issued. A QSP in current flying practice on any
military aircraft type (aeroplane for re-issue of
aeroplane licence and helicopter re-issue of helicopter
licence) may have their licence re-issued by holding a
valid medical certificate appropriate to the licence being
re-issued.
Applicants who are not flying an aircraft endorsed
within their UK or JAR-FCL licence may not have their
licence renewed until such time as an appropriate valid
medical certificate and Certificate of revalidation are
obtained. Applicants may either renew an existing
rating within their UK or JAR-FCL licence or may wish
to transfer a type/class rating that he/she is currently
flying under the privileges of their non-UK ICAO
licence. Renewal of appropriate ratings or the transfer
of type/class ratings is specified in Section F.