In the broadest possible sense by transferring half a house - with or without money - you are "selling" it. The Stamp Duty rules are very complicated (the explanatory book runs to over 800 pages) and so it is necessary to check exactly where you stand before activating your proposal. If the Stamp Duty bill is more than people can afford then sometimes this proposal is abandoned. However, if you do proceed there is no escape. The Land Registry can do absolutely nothing without a Stamp Duty Land Tax certificate whether or not Stamp Duty is payable, and to obtain one you have to declare all to the Stamp Duty Land Tax office.