Hillside Revisited 3 – Sage Advice – Development pursuant to a planning permission does not need to be completed to be lawful

United KingdomScotland

In the third in our series of Law-Nows looking at the Supreme Court’s judgment in Hillside[1], we consider how the Supreme Court has clarified the applicability of the Sage[2] principle. The Supreme Court has now confirmed that development pursuant to a planning permission does not need to be completed to be lawful.

The Sage principle

Sage concerned the time period for enforcement for works carried out without planning permission. Mr Sage had partially built a dwelling house without planning permission and the local authority sought to take enforcement action in respect of the works.

The Court held that there was a continuing breach of planning control as the house had not been completed, and therefore enforcement action could be taken. The four-year time limit would run from the date on which the building works for the whole house were substantially completed and not (as Mr Sage had argued) the completion of the specific operations which constituted the breach of planning control.

The Court also held that a holistic approach should be applied when considering the 1990 Act[3], and the totality of the operations which the person originally contemplated and intended to carry out must be considered.

Hillside – the Court of Appeal

In the Court of Appeal’s consideration of Hillside, it commented on the Sage case, stating that “it has now become clearer than it was before 2003 that a planning permission needs to be implemented in full. A ‘holistic approach’ is required.”[4] This comment gave rise to the suggestion by some that development permitted under a planning permission would need to be carried out in its entirety before the development (as a whole, including those parts already constructed) would become lawful. The practical implications of this ‘holistic approach’ were significant and at odds with the general principle that enforcement cannot be brought against development that was lawfully carried out (see our previous Law-Now on the Court of Appeal judgment).

Hillside – the Supreme Court

The Supreme Court made clear that it did not agree with the argument that “if a proposed development is not or cannot be completed fully in accordance with any planning permission under which it is carried out, the whole development [including any such development that had already taken place] will be unlawful.”[5]

The Supreme Court distinguished the Sage case, making clear that the holistic approach should only be taken when considering whether the time limit for bringing enforcement action has begun. Building operations carried out without planning permission are not substantially completed until construction of the whole building is substantially completed.[6]

The Supreme Court highlighted that a local planning authority’s remedy in circumstances where a development has only been partially completed is not to bring enforcement action, but rather to serve a completion notice under section 94 of the 1990 Act (and, even then, failure to complete the development within the required period only invalidates the planning permission going forward).[7]


Development pursuant to a planning permission does not need to be completed to be lawful. This is particularly helpful for multi-unit developments; a failure to build out all of the units permitted under the permission does not endanger those already constructed.

Look out for our future Law-Nows in this series, which will discuss other key points coming out of the Supreme Court’s Hillside decision.

[1] Hillside Parks Ltd v Snowdonia National Park Authority [2022] UKSC 30.

[2] Sage v Secretary of State for the Environment, Transport and the Regions [2003] UKHL 22.

[3]Town and Country Planning Act 1990.

[4] Hillside Parks Ltd v Snowdonia National Park Authority [2022] EWCA Civ 1440, [65].

[5] Hillside Parks Ltd v Snowdonia National Park Authority [2022] UKSC 30, [56].

[6] Ibid, [62].

[7] Ibid, [63].