When the NPPL was being formulated, a lot of comments were made along the lines that contemporary Microlights often out performed the old 1950s combine harvester engined spamcans of the SEP world - and yet Microlight training and licensing requirements were less onerous. So why not make SSEA (or 'simple SEP' as it was then) licensing as simple?
However, it was pointed out that rocking such a boat was inadvisable. Because the high-performing Microlights were rather removed from those devices which looked like an illicit affaire between a tent and a strimmer which were around when the PPL(M) first came in. "Keep going on about how much more performance these gucci Microlights have than a C150 and you'll find yourselves regulated as a C150 pilot would be!" was one comment.....
There will always be aircraft which are right on the borderline of some regulation - such as 1999 kg certified twins which avoid 2000 kg €urocharges.
There isn't really a clear solution to this, regrettably. Would that there was!
You cannot train for an NPPL SSEA in a Eurostar EV97A because it is a home-built. On the other hand, you can train in it for a JAR PPL if you own it and already have an NPPL SSEA
Are you sure? ORS4 No 802 specifically states
Flying training excludes instruction in flying given for the purpose of becoming qualified for the grant of a pilot’s licence or the inclusion or variation of any rating or qualification in a pilot’s licence.
Also see JAR-FCL 1.125(b)
Flight instruction. An applicant for a PPL(A) shall have completed on aeroplanes, having a certificate of airworthiness issued or accepted by a JAA Member State, at least 25 hours dual instruction and at least 10 hours of supervised solo flight time, including at least five hours of solo cross-country flight time with at least one cross-country flight of at least 270 km (150 NM), during which full stop landings at two aerodromes different from the aerodrome of departure shall be made. When the applicant has been credited for pilot-in-command flight time on other aircraft in accordance with JAR–FCL 1.120, the requirement for dual instruction on aeroplanes may be reduced to not less than 20 hours.