On the A55 in North Wales near LLandudno and Colwyn Bay there are stretches where it has a 50mph speed limit and that's shown by a conventional circular sign with 50 written on it in a red circle with a white background.

What puzzles me is that when the 50 limit ends instead of there being a National Speed Limit Applies sign (white circle with a black sloping bar through it) they have a 70 sign in the same style as the 50 sign.

Is there any specific reason for this? It occurred to me that it MIGHT have something to do with that road being used by foreign lorry drivers coming from Holyhead?