but unless that's the case you'll need to complete a check flight with an examiner and submit the relevant forms and possibly a fee to the CAA.
No fee in 'cheechm's case. An appropriate Examiner can renew most Ratings (on a UK Licence) provided the Rating has not expired by more than 3 years. It is also the Examiner's responsibility to submit the forms (within 14 days), not the candidate's.
It is only when the CAA itself has to Renew a Rating that they charge a fee.
A lot of European NAAs do not authorise Examiners to do this 'in the field' and therefore Rating Revalidation or Renewal can cost a lot of money (Germany springs to mind).
It is for this reason, I believe, that the LAPL was designed with a Rolling Validity, rather than expiring Ratings