Muffin,
You are right and wrong at the same time
. As TTH's says, with a
UK PPL (CAA) you
don't need any formal training (due to grandfather rights). However, if you have a newer Euro PPL, then as you say, you do need differences training to fly a microlight. The tailwheel differences applies to both unless you have previously flown tailwheel. In either case you'd be daft not to have a good checkout, as there is considerable difference in inertia between most microlights and typical group A aircraft.
SS