Developers must act to minimise the risk of causing actionable interference with rights of light to adjacent buildings.

The development of land or the increase in height of an existing structure both risk interference with existing rights to light. Well advised developers should consider the age of buildings surrounding their own site so that they do not miss the opportunity to prevent rights from being acquired.

In the absence of any contractual agreement to the contrary, the apertures in a building will acquire a prescriptive right of light under the Prescription Act 1832 after 20 years' continuous enjoyment. In order to stop such a right arising, a developer can put up an actual obstruction, such as a screen or a building. However, the Rights of Light Act 1959 provides a much quicker and cheaper method of interrupting the enjoyment of light by allowing for the erection of notional obstructions by way of Light Obstruction Notices. In most cases the notional obstruction will take the form of a screen of infinite height. Due to legal technicalities, a physical or notional interruption must commence within 19 years and 1 day of the start of the prescriptive period in order to prevent rights from being acquired.

A Light Obstruction Notice may also be used as a means of identifying and potentially extinguishing rights to light which already exist. Once the notice has been registered, the affected neighbouring owners have one year to assert their right to light by the issue of legal proceedings. If the notice remains unchallenged after one year, the right to light is deemed to have been interrupted and the 20 year prescriptive period will start again from zero.

Therefore, even if a developer is too late to stop rights arising, it may be worth using the mechanism under the Act to flush out any potential claims. If neighbouring owners fail to challenge the notice, the developer's position will be strengthened.

This is also something building owners might consider in order to enhance the value of their properties even if they have no immediate plans to develop.

The process under the Act is relatively painless and involves an application being made to the Lands Tribunal for directions as to what steps must be taken to notify those who will be affected by the notional obstruction. Copies of the application must then be served on those directed to be served. Once satisfied its directions have been complied with, the Lands Tribunal will issue a definitive certificate that allows for registration of the notice as a local land charge.

If a building may be close to acquiring enjoyment of 19 years and 1 day, it is also possible to invoke an emergency procedure and register a temporary notice, in order for the obstruction to commence as soon as possible and allow time for a definitive certificate to be obtained.

The only area of uncertainty is whether the procedure described would block a claim to a right to light under the fiction of lost modern grant (which is a common law method of asserting that a right of light exists). This point has not been tested and the law requires clarification in this regard. However, even if a right could be asserted under lost modern grant, it seems likely that a failure to challenge a notice would affect the ability of a neighbouring owner to obtain an injunction, which would be a valuable outcome in any event.