I am totally open to correction on this (in case I get any facts and figures wrong
*To fly a microlight you need a PPL (M)
*To get a PPL(M) you need 25 hours dual instruction, and 15 hours solo, plus cross country flights as with PPL(A)
*This entitles you to fly a microlight : fixed or flex, depending on which you trained on.
Now as far as I know, 15 of those 40 microlight hours count towards your PPL(A). You just need to do the cross countries again.
*PPL(A) syllabus requires that you do 5 hours instrument training, so you'll need to do that as it wont have been covered on (M)
The ground school is the same, and you'll have that done.
Smoke me a kipper, I'll be back for breakfast.