I'm from the UK...but I've never registered for tax because the only money I get from YouTube is well below the personal allowance. Heck, my AdSense doesn't even reach my custom threshold every year; it takes me 2-4 years to get there, and I'm not working a job in the offline world.
So I decided long ago that if HMRC wants to attach the penalty for not registering, they can go ahead and do it.