If I sell my property which is my primary residence to a developer and they pay 25% above the market value for the property, do I have to pay tax on the amount that they pay in excess of the market value, or is all of it tax-free as it is being paid for my primary residence? 

Arthur Weller replies:  

If you have lived in your property as your main residence all the period of your ownership, so that it is fully eligible for principal private residence relief, you do not have to pay any capital gains tax on its sale, even if the purchaser is paying above market value.