(d) If the IR has not been revalidated or renewed within the preceding 7 years, the holder will be required to pass again the IR theoretical knowledge examination and skill test.
However; FCL.010 says
"Skill test" means the demonstration of skill for a licence or rating issue, including such oral examination as may be required.
Having held the rating already, it must be a Prof Check
"Proficiency check" means the demonstration of skill to revalidate or renew ratings, and including such oral examination as may be required.
In the days of old, the UK CAA required an initial re-test if the IR had expired more than 5 years. One could interpret:
to pass again the IR theoretical knowledge examination and skill test.
as meaning an initial IR skill re-test with an IRE is required.