Portsharbourflyer is right: while one needs a valid ME/IR (SPA) before starting a type rating on a multi-pilot aeroplane, once the type rating LST has been successfully passed, you are issued with a shiny ME/IR (MPA) rating, therefore there is no need to keep the ME/IR (SPA) current.
Also, remember that the CAA now requires that every other ME/IR (SPA) renewal should be done in the actual aircraft, therefore requiring more money; however, if you renew your ME/IR on the aircraft, you can combine the IR renewal flight with an MEP renewal and kill two birds with one stone.
In a nutshell, a type rating does not extend an ME/IR (SPA), it replaces it.
Cheers