HMRC is targeting homeowners who have sold buy-to-let properties or second homes without declaring profits and paying capital gains tax, by offering lower penalties for voluntary disclosure by August 9th, but threatening higher penalties if caught later. Those selling non-primary homes in the UK or abroad could face capital gains tax if profits were made. This campaign aims to recover unpaid taxes on home sales outside of primary residences, including rental properties, holiday homes, or homes sold as gifts.