I've lived all over (Shropshire, Wales, Yorkshire, Manchester and London) and find it differs greatly.
For me it's breakfst, lunch and tea though dinner if it's going out or something posher like having friends round for dinner. Supper is used back home as a late evening snack after tea.
In Manchester my lunch seems to be more commonly dinner which is strange to me though thinking about it growing up in Shropshire we always had school dinners (or lunchbox), dinnerladies etc...at lunchtime.