I believe the original nano Brompton battery was 266w. So technically illegal by European standards, but one wonders how this is enforced. "Freeze! Battery police! Take your hands away from the handlebars slowly..."
I suppose if you were in an accident, it could become an issue, but otherwise, it's not exactly like the nano Brompton was a speed demon. I'm not condoning breaking the law, just pointing out the obvious.
For anyone who wants to read a good review of the original nano Brompton from my fave
A to B magazine:
Nano Brompton Folding Electric Bike Review | A to B Magazine