I *think* that you'll need to re-take air-law, training as required, NPPL medical (basically just a self declaration) and then an NPPL(M) skill test.
I *know* that if you phone the BMAA on 01869-338888 in working hours and explain the problem, they'll have somebody there who is absolutely up to speed on this, can quote chapter and verse, and also tell you where the nearest good microlight school is. If you're in Uxbridge however, the answer to that is probably Wycombe Air Park on a Eurostar.
G