If you have 500 hours of multi pilot time on a recognised multi-pilot aeroplane you are exempt. Please note that dual time does not count.
However, if you fly for an operator that operates a single pilot aeroplane (like a Caravan) as a multipilot aeroplane then that counts, too. We had an enquiry from someone who flew Caravans for a freight company who put two pilots on their aeroplane, and as the local aviation author¡ty recognised the this as multipiot time, then they were exempt the MCC. But, the local authority has to recognise the flying as multipilot time - unless they do the time won't count.
It's all in LASORS, just not sure which page!