Interesting question and I think it's a grey area. If I was asked I would want to check directly with the CAA about their official position.
As you have said, suitably trained engineers don't need a pilot's licence because when taxying for maintenance purposes there is no intention to fly.
The CAA might say you would need to complete training, same as the engineers (yes, I know, no real logic, only a backside covering, rubber stamping exercise. The course would probably held by a pilot who has lost his medical cat)!
This wouldn't apply to helicopters (even wheeled undercarriage ones) because they are considered to be flying as soon as they first move under their own power.