It's impossible to contact Burgess without a phone number so it's not that easy to find out.Made in the UK or not the ingredients can be sourced elsewhere(not saying all are,but it's completely possible that they could be and without knowing the safety level goes down).
However,I do know that dried mealworms in particular are incredibly difficult if not practically impossible to find from sources other than China.This information is pretty easy to find,whether it be the country of origin of a product(or where it's made)or something that a manufacturer of a specific product states.Sourcing on UK products is much harder to find,and even if a product is made in a certain country it can still outsource ingredients as mentioned before
I'd honestly love to be proven wrong and find that there was one magical non-Chinese source of dried mealworms if nothing else(neither sourced nor made in!)but after digging fairly deep a while back the likelihood just isn't there.Even then,the chances of Burgess actually sourcing from a non-Chinese mealworm source are going to be low,and there could still be some very weird and completely unexpected ingredients sourced from China!