Use a limited company. Use the HMRC website for help on limited companies and get a good accountant for doing your taxes. Mixing your website income and personal income may make you pay a higher tax rate.
You can take out expenses from the limited company, which are tax deductible. But if you group it in personal income it wouldn't be tax deductible. In a personal capacity you are 100% liable if your business goes bust and you owe debt. But for a limited company you are only liable for what you own i.e %age of shares. You can take on an investor if your business booms and it is easier if you do it through a limited company rather than through a personal endeavour.