Alan Webb

Look here - https://www.gov.uk/report-and-pay-your-capital-gains-tax That will walk you through the computation You will need details of: A - Sale price and costs of sale (estate agent and solicitor) B - Original purchase price and associated costs of purchase (solicitors etc) C - cost of any improvements to the property D - an estimate of your income for the year A - B - C is your gross gain D will set the rate of tax Follow the walk through on HMRC system and it should get you there, or ask an accountant

Ask an accountant but though cash basis is default as mentioned by HMRC, you can elect out of that and to adopt the receipts basis instead which may be of benefit as regards relief for mortgage interest paid.

If you have not submitted the return yet and your income was less than £1,000 then you should ask HMRC to cancel the returns required under s8B TMA 1970. If they agree, which they hopefully should, then the requirement to make a return is withdrawn and any penalties cancelled. You cannot make the request if you have already submitted the tax return as it is too late to do so, but if the HMRC Helpline tell you that you must submit a return and then appeal a penalty, rather than them withdrawing the return under s8B that is not the way as it will technically put you in an unappealable position.