i'm on the isle of man but the pellets available are same as in the uk.
i feed supreme science and beaphar care+ - they used to be on supreme science but then i got a rescue with teeth problems and the beaphar care+ is a different type of pellet, it's crunchy (doesn't crumble) and is apparently made to mimic bark so it wears their teeth down better than normal pellets - she loved them so much that i thought i'd give a few to the other chins and they love them. they are quite expensive compared to the other brands available (1.5 kg bag - £9.50, supreme science is 2kg for £5) but i've had fantastic results with mae so she gets mostly them and some supreme science and the healthy chins have two bowls.
as people already mentioned, if what you're feeding is quality food and it has the right levels of nutrients (ie not too much protein or fat), you can just continue with that. if you do change food, just make sure you do it very very slowly, i usually do it over a month period.