You wouldn't own the land. It's quite common with small business web design for the developer to also control the hosting. The actual point in the web site case is that you are revoking the copyright license to the content until you receive payment, a well tested and accepted concept in UK law.

That said, there have certainly been situations where builders have gone back to properties and taken back their property (like tiles from walls, joinery, etc.) but I have no idea how that pans out legally as it's outside my wheelhouse.