I don’t know many brands of food from the UK, but what you have to pay attention to is that the main ingredient is natural animal protein, that it does not contain so much flour and artificial proteins.
Hello. Keep your puppy on the same food that the breeder has given, at least until she is settled in your home. Markus Muhle is a cold pressed food that is good quality and economical. It can be found on Zooplus who also sell Lukullus. They are not grain free but contain brown rice which has nutritional qualities for dogs. Markus Muhle and other cold pressed dog food.
If you want to go grain free, have a look at the higher rated extruded foods in the dog food directory. You mention budget but sometimes paying more can be cost effective because the higher quality ones have more protein in them so you won’t have to change food as puppy grows. Also, it is sometimes the case that when the dog becomes adult it requires smaller amounts.