If you operate a radio, you need an FRTO licence. Private flying from an unlicensed strip in G airspace, there is no need for a radio. However it's not much of a course to do, and will expand your opportunities.
Here is the CAA's list of radio examiners.
Revalidating the PPL will be a skills test with an examiner. Lasors section F1.5;
F1.5 RENEWAL OF SINGLE-ENGINE PISTON
– SEP (LAND), TMG CLASS RATINGS
Where licence holders have been unable to renew a
SEP (Land) or TMG Class Rating for a period not
exceeding 5 years from the date of expiry, they will be
required to complete the following requirements:
i. The CAA will require no mandatory additional
training. Applicants should complete training at
their own discretion sufficient to pass the Skill
Test.
ii. Complete the Skill Test in accordance with
Appendices 1 & 3 to JAR-FCL 1.240 with a JAR
Authorised Examiner. For renewal of an
instrument rating if held, please refer to Section
E1.5.
iii. Pass an oral theoretical knowledge examination
conducted by the Examiner as part of the skill
test.
iv. A UK Authorised Examiner can sign the
Certificate of Revalidation page (FCL150CJAR)
within a UK national pilot’s licence. An Examiner
qualified in accordance with JAR-FCL (in any
fully compliant JAA Member State) can sign a
Certificate of Revalidation page within a
JAR-FCL licence. The LST/LPC form, completed
as a renewal, should be sent to CAA PLD.
v. The CAA will charge no fee provided that the
Examiner signs the Certificate of Revalidation.