Rich,
50 hours PIC means that you must have 50 hours as pilot in command before the IR application, the time under instruction on the IR course DOESN'T count towards this. You will need to fly P1 for at least 40 hours after the PPL (you should already have 10 hours PIC x-country from the PPL training).
If you do a single engine IR this DOESN'T allow you to then have IR privledges on a multi engined aeroplane. You would have to do another test as the CAA needs to see a demonstration of Assymetric (engine failure) procedures on the multi. I do not know for sure but I think there is a training requirement of around 15 hours multi IR training before being able to take that test.
Hope this helps.
