Plans to be determined objectively
 UKSC 13
The meaning to be given to the key wording in a development is not a matter that can be left to the judgment of the planning authority. Nor is the interpretation of policy that it sets out primarily a matter for the decision-maker. Plans are to be determined objectively.
Tesco sought judicial review in the Scottish courts of the decision of Dundee City Council ("DCC") to grant outline planning permission for an Asda retail and food superstore on the outskirts of Dundee. Tesco operated a similar facility around 800m from the proposed Asda site.
DCC decided that although the proposal was contrary to employment and retail policies in the structure and local plan material considerations indicated that permission ought to be granted in any event. One of the relevant policies expressed the usual sequential approach to selecting sites for retail use whereby the retail use should only be permitted in the out-of-centre sites if no suitable site is available in the first instance within and thereafter on the edge of the City Centre or District Centre.
In their application for judicial review Tesco argued that DCC had misunderstood the meaning of the word "suitable" in this policy in that they had interpreted it to mean "suitable for the proposed development" instead of "suitable for meeting identified deficiencies in retail provision in the area." The Lord Ordinary dismissed Tesco’s appeal. His ruling was upheld on appeal to the Second Division. Tesco appealed to the Supreme Court.
Counsel for Tesco and DCC agreed that the question of what words in a development plan policy are capable of meaning was a matter for the court to determine. If the planning authority attached a meaning to words that they were not capable of meaning then it would make an error of law and fail to understand the policy. This is certainly the conventional understanding of the way that challenges based on a misunderstanding of policy operate.
Decision of Supreme Court
The Supreme Court rejected this approach. Lord Reed said that the development plan was a carefully drafted and considered statement of policy and was intended to inform the public of the approach that planning authorities will follow in determining planning applications. It therefore guides the behaviour of applicants and public bodies. The existence of the development plan is designed to ensure a consistent exercise of discretionary powers. Therefore he held at  -  that:
- "Those considerations point away from the view that the meaning of the plan is in principle a matter which each planning authority is entitled to determine from time to time as it pleases, within the limits of rationality. On the contrary, these considerations suggest that in principle, in this area of public administration as with others, policy statements should be interpreted objectively in accordance with the language used, read as always in its proper context."
Lord Reed echoed Davis J’s observations in Cranage Parish Council v First Secretary of State  EWHC 2949 in saying that "…planning authorities do not live in the world of Humpty Dumpty: they cannot make the development plan mean whatever they would like it to mean."
Lord Hope at  expressed the ratio of the case as follows: “The meaning to be given to the crucial phrase is not a matter that can be left to the judgment of the planning authority. Nor is the interpretation of policy which it sets out primarily a matter for the decision-maker.”
In the event the Supreme Court held unanimously that DCC’s interpretation of the word “suitable” had been the correct one and the appeal was refused.
This case signals a different approach to challenges based on misinterpretation of policy. The upshot is that henceforth such challenges will be about errors of law rather than Wednesbury irrationality.
Weight to be accorded to “old” policies
 EWCA Civ 1146
The mere age of a policy does not cause it to cease to be part of the development plan. The weight to be given to policies in a development plan might vary where circumstances have changed over time, in particular if there had been a significant change in other relevant planning policies (such as the NPPF) on the same topic.
The developer's application for planning permission was directly in conflict with local plan policies adopted in 1997 and saved in 2007, and the local authority refused planning permission on that basis. However, the planning inspector allowed the developer's appeal on the basis that the policies should be given reduced weight because of their age. The Council applied to the High Court to quash the inspector’s decision under s 288 of the Town and Country Planning Act 1990 on the basis that he had failed to properly assess the weight of the local policies in accordance with the NPPF.
The High Court quashed the inspector's decision on the basis that the inspector had failed to properly assess the weight of the local policies in accordance with para 215 of the NPPF. The developer appealed to the Court of Appeal.
Decision on appeal
The Court of Appeal dismissed the appeal and upheld the decision of the High Court. The mere age of a policy does not cause it to cease to be part of the development plan. Significant weight should be given to the general public interest in having plan-led planning decisions even if particular policies in a development plan might be old. The starting point for decision-making is s38(6) of the Planning and Compulsory Purchase Act 2004, which required that decisions should be made in accordance with the development plan. This includes old policies, unless material considerations indicated otherwise. A significant change in relevant planning policies or guidance dealing with the same topic may mean that a policy is outweighed by other material considerations. In that regard, old policies should be assessed for consistency with the NPPF and its policies, which is provided for under para 215 of the NPPF.
The above explains the general approach to be taken when assessing the weight to be accorded to old policies. The Court recognised that a separate process applied under para 49 regarding relevant policies for the supply of housing where a local planning authority cannot demonstrate a five-year supply of deliverable housing sites.