For canned/wet food, protein % isn't really a meaningful statistic. This is because mostly what that's telling you is how much water is packed in with the meat. Even for dry food, it's also, by itself, not a very telling statistic, because manufacturer's can achieve a high percentage by stuffing food with horrible stuff like animal by-products and rendered meat.
I think for wet food, the best that you can do is look at the ingredients list, and see to what extent there is "bad stuff" in there (see links below for articles on this). Imo though, as I've grown more and more cynical about pet manufacturer's and their abilities to lie and deceive about ingredients, I think actually looking and smelling the food might be the best way to get a read on it. If it looks and smells like human-grade food, then it probably is. If it's an unrecognizable gruel of thick brown paste, I immediately cross that off my list. Who even knows what could be in there?
I'm in the US, and not familiar with Butcher's brand, but after some quick googling, they seem to be strangely reluctant to share their nutritional info. The one place I could find with supposidly nutritional information, list their ingredients as "Meat & Animal Derivatives" LOL...owch.
Whiskas has always been a pretty crappy brand imo. I suggest browsing through the "nutrition" section of this site (especially a few years back). There used to be a ton of posts from people from UK talking about cat food options. Some fierce battles were waged and some great discussions were had.
I really like this site too:
https://littlebigcat.com/nutrition/This might be of particular interest:
https://littlebigcat.com/nutrition/sele ... -pet-food/