We'll agree to differ on terminology. To me "on the ward" means you haven't left the confines of the space enclosed within the ward doors and that includes non-patient areas such as the treatment room, secretary's office, doctor's office, nurses' office and yes, "salle de repos" which can be translated as rest room. In France we have a single room culture, not open bays, so there aren't patients and relatives wandering round as is common on British wards. They usually stay in their rooms and if they want something or have a question they ring.
You may consider it bad management to just have two nurses on a night shift but the reality is, nobody is going to put 3 or 4 nurses on nights for a 12 bedded ward in either country. I am often on nights with one other nurse. When (s)he is in the rest room on break I will only ever disturb him/her for a dire emergency, however I'm comforted that they're there if needs be and not 7 floors away in the canteen. I remember being left alone on wards in the UK and yes, that is bad management.
If as you suggest, the ward area got so busy that your breaks were disturbed on a permanent basis, believe me that would be addressed in France. I agree it probably wouldn't in the UK. The fundamental difference between the two countries is that while you had years of Thatcherism the French had 14 years of Mitterand's socialism and that has fundamentally affected the directions our two nations have taken since and the state of public services today. I've been in France nearly 20 years - I appreciate my paid break, the free meal, and since it rarely gets disturbed I don't mind having it within the ward doors. I essentially still get my break away from the patients with all the benefits you describe. I occasionally get disturbed for a real emergency - so what, I'm being paid and my colleague hasn't been left in the merde. Yes, I do believe that is a more civilised way of organising healthcare. British nurses are used and abused - I've been there. I don't feel abused in France. I speak from experience. I never said it was civilised to not get a break. I said it was civilised to get a paid one, and if I very occasionally sacrifice it to help a colleague that's fine. Believe me, if it was ever abused, French unions would be on it.