Thanks for these replies. I think a few points are raised. While clearly to take an initial IR one needs the MEP class rating. However, if a renewal were done in a simulator, would the class rating still be needed as the "flight" is not actually done in an aircraft?
While this would obviously mean that the full privileges of the licence (i.e. to fly an MEP in IFR) could not be exercised, it would appear that the requirement to hold a Multi-IR in order to undertake a type -rating would be fulfilled.
Whilst having the MEP rating would be preferable, the chances of getting a Seneca type job with my low hours is non-existant, so I would like to be able to renew the IR using the cheap simulator option whilst retaining all the qualifications necessary to start a type-rating course if any jobs do appear.