UK Construction and Law

Both challenges to the Gatwick northern runway order are refused permission to appeal, and the wastewater condition survives

By Staff Writer  |  28 August 2026

The Court of Appeal held every ground unarguable and dismissed both applications. The requirement governing wastewater stands, including the words allowing Thames Water to agree something else in writing, which the court held was not the unlawful kind of tailpiece. The decision was certified as citable.

The development consent order was made on 21 September 2025. It authorises the improvement of the northern runway at Gatwick and the lifting of the restrictions that prevent the northern and southern runways being operated as a pair, together with airfield works, terminal works, hotels, offices, car parking and surface access improvements. Two claimants challenged it under section 118 of the Planning Act 2008. Their claims were heard together at a rolled up hearing in January and dismissed in June, and the applications for permission to appeal were refused on 4 August.

Policy is not read like a contract

The first applicant's case was that the airports policy statement, in endorsing a north west runway at Heathrow, did not support expansion of capacity at Gatwick, so the proposal had to be assessed as a departure from policy rather than in accordance with it. The court treated that as a question of interpretation and set out how such documents are to be approached.

The task of interpreting policy should not be undertaken as if the policy were a statute or contract.

Lord Justice Holgate and Lord Justice Dove

Policies may contain broad statements of principle that appear to conflict and have to be balanced. They are written for expert professionals and the wider public alike, for practical decision taking across a wide range of facts, and they are read as a whole. Weight, and the judgment involved in applying policy, remain for the decision maker.

The wastewater requirement, and the tailpiece

The ground of most practical interest to anyone drafting requirements concerned foul water. The scheme will generate additional flows that must be taken either by the existing network or by new treatment works, described in the order as Work No 44. Requirement 31 obliges the undertaker to give Thames Water a development phasing plan with forecast passenger numbers and detailed discharge forecasts, validated by the water company in writing. The company then has twelve months to confirm whether its infrastructure can take the flows for the ten year period after dual runway operations begin. Those operations may not start until either the new works are complete and an environmental permit application has been submitted, or the company confirms the existing network can cope.

The objection was that this leaves room for the scheme to start operating without the infrastructure in place: the requirement does not compel a permit to have been granted, nor the new works to be operational, nor the operator to use them once built. The court was unpersuaded, describing the concerns as farfetched. If the works have to be built, it is reasonable to assume the design will be fit for licensing, and that a party which has spent a substantial sum building treatment works will use them.

In assessing the need for and formulation of the requirement the SST was entitled to assume that the EA, TWUL and GAL would act rationally.

Lord Justice Holgate and Lord Justice Dove

The separate attack was on the closing words, that the position may be otherwise agreed in writing by the water company. Tailpieces of that kind have been held unlawful where they carry no limit and could allow development materially different in scale and impact from that applied for. Here the court held the point was not engaged. Any use of the words would have to serve the object of the requirement, which is adequate treatment of waste water, and the order contains a general provision that an approval of that sort may not be given unless the discharging authority is satisfied the departure gives rise to no materially new or materially different environmental effects from those assessed in the environmental statement. That general provision is the answer, and it should be looked for whenever a similar form appears elsewhere in an order.

What survives

The climate grounds did not succeed either. The decision maker was entitled to rely on the aviation decarbonisation policies and their monitoring and revision arrangements, and was not obliged to take account of every periodic return that tracks progress against them. The court held that each ground raised by each applicant was unarguable, that neither appeal had a real prospect of success, and that there was no other compelling reason for either to be heard. It certified that the decision may be cited as an authority, which is the part promoters and objectors will use. On this record, a requirement that sequences an operational start against a statutory undertaker's confirmation, and that carries a properly constrained ability to agree an alternative, will hold.