
The basic requirements are:
To register with HMRC as self employed - This means filling out a self assessment form each year with your income from the business and your job.
If you are not paying any contributions then you still have to register to pay class 2 (or depending on your circumstances another class x) contributions to HMRC
As a seller of jewellery you have to comply with EU nickle directives and the lead content directives depending on when we join that as a member state. If you use sterling silver, gold, platinum or palladium, you will need to comply with Hallmarking Law.
If you sell over the internet, phone or other non-face to face medium you have to comply with the Distance Selling Regulations.
As a retailer you will have to comply with the Sale of Goods Act (some parts of which are overridden by the Distance selling regulations, like cancellation and returns).
If you intend to run a website you may have to comply with the EU cookies directive.
Those are the basic ones to be aware of. Depending on what you do and how you do it, there may be others.