Rights of light can be acquired by prescription if for 20 years an identifiable channel of light has benefited the neighbouring block. This can be prevented by interrupting the 20 year period before the expiry of 19 years by lodging a notice of notional obstruction with the Lands Tribunal where it is certified. An application is then made to the local authority, and the notice is entered on their local land charges register for a year. Your neighbour&amp;’s 20 year period would then be interrupted and the clock would have to be re-started to acquire any rights. The notice of notional obstruction basically states the dimensions of a theoretical obstruction that might (but never is) built to cut off light to your neighbour.<p></p><p></p>