Most important is a balanced diet. So while fruit and veg are important so are other things in a diet. If he is eating fruit at the expense of proteins, meats, dairy, and cereals, then you'd want to cut down. Each country has it's own method of "balancing" a diet - for instance in Canada it is a "Food Pyramid" and your personal food pyramid depends on your age, gender, etc. A 2yr old toddler needs 4 serves of Fruit and Veg, 3 servings of cereals, 2 servings of dairy and 1 serving of meat/meat alternatives. Serving sizes are spelled out in the food pyramids, etc. I am most comfortable using the Canadian food guidelines, but you can look up the UK healthy eating guidelines for toddlers and see what they advise. I know in the UK it's "5 a day" but serving sizes are smaller for kids than adults, once he's hit his 5 a day, I would try to get him to eat other things to balance his day/week out (we aim for a healthy week moreso than a healthy day).
It's probably more important to change up his fruits often and have him eating a variety to expose him to different nutrients than it is to just make sure he eats loads. Ie/ if he is eating the same 4 or 5 fruits all the time it's getting the goodness of those things into him but a wide variety all the time is best.
