What Whopity said, you do not need to hold a valid medical certificate to undergo a proficiency check. The Flight Examiners Handbook states:
Checks, tests and assessments of competence for rating or certificate issue, renewal or revalidation may be carried out on individuals whose licence or medical is out of date. However, before the flight, the examiner must point out such discrepancies to the applicant and explain that, irrespective of the result of the flight test, the applicant will not be able to exercise the privileges of the rating unless and until the medical certificate and/or licence has been renewed.