Yep, make sure you have the clearance, listen out for the magic of ".. .. you are cleared .. .." and if you dont get it ask.
The discipline is a good one because somewhere else you will make the same assumption, only to find that the controller feels strongly otherwise.
Be equally careful in France. It is even easier to assume you have been cleared. A good friend of mine thought he had, not least because he had called the unit concerned on a number of occasions without response, so assumed they were closed. He proceeded without the clearance. He was reminded of his transit when he received a letter from the CAA following up one form DGAC.