There is a simple upgrade route however from NPPL(M) - the microlight licence, to NPPL(SSEA), which actually provides the majority of what most PPL holders want - the ability to fly 4 seat light aeroplanes, in visual conditions, for fun, in UK airspace.
CAA are threatening an NPPL--> PPL upgrade route again soon, and they might actually do it.
So for somebody who just wants to fly for fun, has no ambitions to fly inside clouds, at night, on instrument approaches, microlights is a great route, just as it has been for 30+ years. Its how I started and I didn't find the subsequent upgrades to light aircraft, multi-engine, instruments etc. all that problematic.
G