Frio seems to be the case of choice, when this question is asked on the forum.
https://friouk.com/
Frio wallets keeps insulin cool. They are not cases for diabetes paraphernalia such as meter, needles, lancets, test strips, etc.
If you google “diabetes case uk” there are lots of options.
Personally, I do not use a dedicated case. I use a
Healthy Back Baglett. This is big enough for two insulin pens, meter (without the case ... I don’t need a case within a case) test strips, lancer, there is a pocket needles and lancets and still room for a credit card, mobile and house key.
If you want to keep your insulin cool because you are going to a hot climate, a two pen Frio wallet fits in the Baglett.