Hi Lister
The differences training answer is correct for a microlight.
The same applies for an SLMG licence which is added to your JAR PPL.
But for glider you need to have a check with a BGA instructor who will issue you a BGA Gliding licence - I believe they act as an 'agent' for the CAA in these matters.
Of course don't underestimate the time or skills involved for each conversion (having done all 3 at some point or another !)
I'd suggest you zip into Tibenham in the Cub (with PPR of course !!) and check it out. I believe there are people there who can do all 3 for you.
I'm sure Jim L can advise you of a contact there.
Regards from NZ
Arc