For me (south of England), dinner is the main evening meal eaten between 6pm and 8pm, and supper is a late-night snack before bed. However, there are plenty of different opinions. My flatmate (Midlands) will say that dinner is eaten at noon or early afternoon, tea is eaten between 6pm and 8pm and supper is a late-night snack before bed. I have another friend who says that the three main meals every day (Monday to Saturday) are breakfast, dinner and supper, but on Sundays she has "tea" - sandwiches, cake and pots of tea at around 4pm.
There is no clear-cut answer to your question, as you can see!