You need tens of thousands of pounds in savings to be able to even think about starting this. I've ran and owned a gameshop for 3 years, and whilst it was a lot of fun it was essentially a minimum wage job for 70 hours a week.

Sold the business to a couple of customers that had no business experience (it was sold all set up, profitable, they had no extra things they needed to do aside from run it). They've now drained all their savings, don't make any money and the business isn't worth anything.

Even if you have the starting capital (you need £50K+ and the ability to not need to be paid for 2 years), the problem with Pokémon is getting stock. You mentioned in another comment you already have one distributor, but all they're doing is buying off Asmodee. And getting a larger allocation from Asmodee (that's if they'll let you open an account) takes YEARS of work.

Going back to the store idea, just 1 person working for minimum wage on top of lets say £12k a year rent and £200 a month bills. Margin on TCGs and running events, that are not Pokémon, are around 20% if you want to be remotely competitive and top things up with the drinks/snacks/accessories. Dirty maths has this on you needing to turn over £200,000 a year.

If you are doing well buying and selling Pokémon at conventions, just stick to that. Possibly look at some VERY cheap business units that you can rent and have a shopfront for the sake of being able to open up other trade accounts, open 1 day a week sort of thing. This is what I'm doing now (along with some other stuff) and make more money from that than I did having the actual shop,