Assuming the property has never been your main home, the gain will be the difference between the net of disposal costs sale proceeds and the sum of the purchase price, costs of purchase and any improvement costs. The first £11,100 of the gain will be tax free due to the annual CGT exemption.
As you are a 40% taxpayer, you will pay capital gains tax at 28% on the net taxable gain. Take a look here for information on CGT.
I hope this helps but let me know if you have any further questions.