The 'authority' is not the yellow lines, but what it says on the attendant signs in the road.
Common place for cars to park on speed bumps where there are no parking restrictions.
In the case above if a Smart car fits (even parked at 90degrees to the kerb) and the attendant signs do not say the parking restrictions also apply to the speed humps, then theoreticallyI consider it would be lawful unless the Police decided an obstruction was being caused.....