BritPilot,
Not sure why you thought it was bi-annual - the single-engine is bi-annual, but not the multi.
Agree with the other replies - all you need is a proficiency check with an examiner. If you have an IR, this should be combined with your IR renewal. The examiner can then sign your license, and the paperwork is sent to the CAA but there is no charge. For the full details, see
LASORS , section F3.
It's also worth point out, for the future, that the requirements for keeping this rating valid are not just a case of hours. You must have completed 10 "route sectors" (a route sector being a take-off, 15 minutes of cruise, an approach and a landing),
and a test with an examiner. If you haven't done the 10 route sectors, you can substitute one route sector with the examiner as part of the (longer) test. Hours don't actually come into it at all.
FFF
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