From Part-FCL page 801
FCL.625 IR — Validity, revalidation and renewal
(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, you are exempt from needing to do anything at all if you hold a UK issued EASA ATPL, as the Brits implemented a derogation in 2013 to this policy. If you don't have a UK issued EASA licence then this may be a loophole worth exploring but perhaps best to wait until after Brexit and see how cordial the relationship is between the UK and EASA.