Sorry for being rude and not replying. I'm reluctant to share too much advice on setting up a business front, as I'm not an accountant or solicitor. I'd suggest you get in contact with a tax accountant who can advise how to best structure your business.
What I will say is if you are selling goods for a profit, you will need to declare that income to HMRC. The chances are that as a 13 year old selling a few bats without another job is that you'll fall under the personal tax allowance bracket.