A perennial thorny planning law question is whether the amalgamation of two or more dwellings into one requires planning permission. In June 2016 some light was shed on this in the High Court case of R on the application of RB Kensington and Chelsea v (1) Secretary of State for Communities and Local Government (2) David Reis (3) Gianna Tong [2016] EWHC 1785. The decision develops the principles in the earlier case of Richmond upon Thames LBC v Secretary of State for the Environment, Transport and the Regions (the Richmond case). The case considered whether the amalgamation of dwellings constitutes a material change of use (under section 55 TCPA 1990) and thereby development requiring planning permission. Section 55 confirms that the subdivision of a dwelling amounts to development but is silent on the question of amalgamation.

By way of background, whether there is a material change of use in buildings which falls within the definition of "development" in section 55 TCPA 1990 depends upon whether there would be a change in the character of the use of the land. This test represents the legal threshold for the application of planning control to non-operational development. However the Richmond case held that whether planning permission is required for amalgamation should be a matter of fact and degree as to whether the loss of an existing use represents a material change having regard to the planning merits of the area, any planning policies in place and evidence of need.

Housing targets in national and regional planning guidance mean that the loss of any housing units, for example due to amalgamation, can have a harmful impact on meeting the demand for new housing. The Royal Borough of Kensington and Chelsea (the Council) therefore considered, on reflection of the Richmond case and in support of the Council's Development Plan which sought to retain and increase the stock of dwellings, that priority needed to be given to increase overall housing supply which outweighed the benefits of amalgamating residential units to provide larger residences in the area. From August 2014, the Council therefore took the view, like many other planning authorities, that the amalgamation of two or more dwellings amounted to development requiring planning permission.

A planning inspector allowed the appeal against the Council's refusal of planning permission and agreed that the amalgamation of the dwellings was not a material change and accorded with the Development Plan, so granted planning permission and the certificate of lawfulness under section 192 of the TCPA 1990. The Council then challenged these decisions in the High Court.

At the appeal the Inspector's response to the Council's resistance to the grant of the lawful development certificate was that the owners amalgamation of two flats would not have any effect on the character of the use of the land, apart from the loss of one residential unit, but he had recognised that the scale upon which amalgamations were taking place in the Borough was having a material effect on a matter of public interest, namely a significant reduction in the number of dwellings in the housing stock. The Inspector had therefore taken into consideration the Council's housing policies for the Borough whilst granting permission and the section 192 certificate. The Inspector compared this to the decision in the Richmond case where the decision was quashed as there had been no consideration of the effect of the loss of dwellings on the local authority area.

In the High Court, the Secretary of State conceded that this has amounted to an error of law; the Inspector expressly disregarded the consideration that the loss of housing units over the next 10 years through the amalgamation of units could jeopardise the Council's attempts to meet the London Plan housing targets, on the sole basis that that need argument was not expressed in and supported by local planning policy.

In this case, the Council was entitled to rely upon their analysis of the effect of conversions upon housing supply as a factor supporting the view that the proposal should be treated as a material change of use and subject to planning control. The Inspector was therefore obliged to consider whether that factor was significant for the specific purpose of deciding whether the proposal fell within the scope of planning control under section 55(1). He was not entitled to decide that question simply by saying that the consideration raised by the Council was unsupported by any planning policy.

Therefore, the decisions to allow the appeal and the grant of the lawfulness certificate were quashed and the appeal will be re-determined by the Secretary of State.

This decision seems to create another 'grey' area of planning law, in which the question of whether the amalgamation of dwellings to form a single dwelling will be in part determined by the prevailing planning policies. This could therefore surely result in a situation where circumstances that amount to a material change of use in one part of the country do not in another.