Yes, get him used to eating proper meals and eliminate some of the snacks. He needs fuel for his body during the day, not just in the evenings.
I'm not from the UK and in my country lunch is the main meal of the day. Breakfast should be consistent too. I'm always surprised at how much food people can eat in Britain for dinner. After 'snacking' all day.
In my school (preschoolers start at 3 and we all ate the same meals - I later volunteered so this is a fact, not my 3yo's vague memory), for lunch kids get:
Salad
First course - something like stew, soup, veg stir fry
Second course - almost adult sized portion of things like pasta, rice, chilli, potato omelette, mini pizzas, veggie burgers, eggs and chips or a jacket potato.
Fruit or yoghurt. Sweet treat on Fridays.
Most kids ate everything. School starts at 9, lunch is 12:30/1pm and parents pick you up at 5pm. Even with a UK bedtime which is right after an early 6pm dinner, if you want less snacking you're going to need more substantial meals.