IO540 is right that old CAA CPL gives you IMC privileges.
I think there is possibly some confusion between single pilot/multi pilot and SE / ME. Your licence should have separate entries for single pilot and multi pilot IRs and these are two sepeaate ratings which must be revalidated separately. Your single pilot IR will almost certainly be a M/E IR. If you renew this on a twin single pilot aircraft you can also revalidate the M/E rating (a separate rating again) at the same time. If you renew on an FNPT II the M/E must be done separately in an aircraft. Renewing your M/E SPA IR gives you S/E SPA IR privileges. If you are in a position where your SPA must be revalidated on the aircraft (ie it has lapsed) you can do it on a S/E but this would then only give you S/E IR privileges (but would be cheaper) you could then at a later date renew on a M/E if you require.
I hope this makes some sense, I am getting my head confused just trying to write this.
MP didn't realise they were changing the rules, however what I have said is how I interpret things at present.