Gary - no matter what your licence, you need a 'Single Engine Piston Class Rating' on your FCL150 in your licence. To keep this valid, you do indeed need to do either 12 hours SEP flying in the second year of the Rating PLUS a 'dual flight with an instructor'. However, any other routine check will suffice for the 'dual flight', so that you could meet this requirement with an OPC for your day job (assuming that it's a JAR OPC). But even if your OPC suffices, if you haven't flown 12 hours SEP in the second 12 months of the Rating, then you'll need to revalidate your rating with a Proficiency Check on a SEP Class aeroplane - the usual steep turns, stallling, PFL, circuits - with a Flight Examiner.
Regards to Bill Dodds!!