Capital Gains Tax is a tax on the profit when you sell (or dispose of) something (an asset) that is increased in value. It is the gain that is taxed and not the amount that you receive and broadly applies to second homes or buy to let investments, not primary residences. Since 6 April 2020, UK residents, individuals, trustees, or personal representatives with a gain arising on the disposal of UK residential property (on which there is Capital Gains Tax to be paid) must report it via the new UK Property tax return within 30 days of completion. It appears that this change has passed by unnoticed and as many as one-third of CGT returns were filed outside of 30 days and in the last six months of 2020, late filing penalties totalling £1,311,300 were issued since the 30-day window was introduced. Read more on this and follow the Government guidance in this article by NAEA Propertymark here.