Well....as a quick glance on the property thread here will confirm, in the following circumstances: - When you've bought a place on the cheap from someone gullible/desperate who didn't understand their property's true value and you plan to flip it in 4 months for a ?100k profit. You don't want to build resentfulness amongst potential buyers or draw attention to the taxman by exposing your quick easily gained profit. You also don't want the world to see you for the money grabbing down rotten filthy parasitic shark you are. - You have sold your house to a family member for way less than market value to avoid stamp, IHT or to effectively transfer capital assets. It will stick out like a sore thumb on the registry and draw attention. For both of the above I'm glad it has to be declared. If yours isn't, the chances are it has been lost in the public sector void where these things go sometimes and just down to sloppy/lazy admin.