Do I have to pay tax if I sell part of my garden?

No, not if you own and live in your house. If it is your “Principle Private Residence” you can sell your house or any part of the land without any tax liability at all – it is tax-free.

If the property is owned by a company or is an investment (for instance, you are a landlord), some Capital Gains Tax may be due. In this case, you should speak to a qualified accountant or your tax advisor.