What business name rules apply to sole traders?

You can trade under a business name instead of your own name without registering it anywhere (unlike a limited company), but you must still include your own legal name and an address for service alongside the business name on invoices, letters and your website. Certain words are restricted or require permission (implying a connection to government or certain regulated terms), and you can't use a name that's the same as or too similar to an existing registered trade mark. It's also sensible to check the name isn't already trading elsewhere to avoid confusion or disputes.