No, the CAA considered that there is nothing in JAR-FCL to prohibit a pilot with a SEP rating from flying a SEP aeroplane below 450 Kgs no matter what else you decide to call it.
JAR-FCL simply says that where ever you see the word "aeroplane" is means aeroplanes which are not microlights and therefore the privilege of the SEP rating according to JAR-FCL is to fly single engine aeroplanes which are not microlights.
What the CAA does within the UK is up to the CAA.
Regards,
DFC