Here are some good links to check out:
You should aim at getting 100% daily value of vitamins per day in one capsule if possible. Some things like vitamin C you should take more than daily value.
Brands are quite different in the UK so I am unsure what you can get. If swansons delivers to the UK, I would check them out because they seem like a good bang for the buck.
I personally use super milk thistle by integrative thereaputics which is very expensive when compared to the other brands ($46/bottle US). Regular milk thistle should work fine.
I would purchase biotin and not a b-complex; once you start eating kefir regularly you won’t need any b vitamins. There are some online resources for people that ship kefir grains to other people in the UK (person to person) and this can start everything for you. If you can get the forum search to work, others have talked about it in the UK.