The Heath & Hampstead Society, R (on the application of) v The City of London & Ors

The Reservoirs Act 1975 is directed to preventing the escape of water from large raised reservoirs, rather than mitigating its consequences through warnings or evacuation. The statutory safety regime requires the professional judgment of qualified civil engineers. Industry guidance may properly inform that judgment, including the use of the probable maximum flood standard where overtopping would endanger dam integrity. Engineers must nevertheless consider material legal, environmental and site-specific constraints when formulating feasible safety measures. Duties to preserve open land or its natural aspect under a local Act do not prevent works authorised by another provision of that Act. A decision-maker may therefore approve preventative reservoir works where the evidence reasonably establishes a serious breach risk, even though the works affect landscape and amenity.

The claimant sought judicial review of the City of London’s decision to approve £17 million of reservoir safety works to ponds on Hampstead Heath and to seek planning permission. The challenge concerned the interaction between the safety regime under the Reservoirs Act 1975 and the City’s duties under the Hampstead Heath Act 1871.

The claimant argued that safety meant a reasonable level of safety, that environmental and landscape considerations had to be balanced against dam safety, and that flood warnings and evacuation reduced the need for preventative engineering. It also alleged irrationality in the assessment of breach risk. The central issues were the statutory purpose of the 1975 Act, the proper role of engineering guidance, and whether the proposed works were authorised by the 1871 Act.

1. Claim dismissed. Permission to apply for judicial review was granted because the claim was arguable, but the substantive claim failed.
2. The purpose of the Reservoirs Act 1975 is to prevent escapes of water from large raised reservoirs and the consequent danger to people and property. It is not concerned with mitigating an escape by flood warnings or evacuation. The existence of other emergency and flood-management regimes therefore did not reduce the defendant’s obligations under the 1975 Act.
3. Section 10 places responsibility for deciding what safety measures are required on qualified civil engineers exercising professional judgment. The ICE guidance was non-statutory and non-binding, but represented recognised industry practice and could properly be applied. For Category A dams, where breach could endanger a community, the probable maximum flood standard was appropriate where overtopping was not tolerable because it could compromise the dam.
4. The engineering assessment was supported by uncontradicted expert evidence. The defendant was entitled to conclude that preventative action was required notwithstanding the low statistical probability of breach. The risk was the consequence of breach, including potential loss of life, rather than merely the probability of breach.
5. Environmental and landscape considerations were material to the manner in which safety measures should be formulated. Engineers had to consider legal restrictions and other relevant environmental constraints, while still securing the required safety standard. The recommendations in this case had in fact sought to minimise landscape and ecological harm.
6. The works did not breach the Hampstead Heath Act 1871. Existing pond, dam and outlet structures were pre-existing development for the purposes of section 12. Section 15 authorised works to drain, level and improve the Heath for health, exercise and recreation, and that power qualified the general prohibition on building. Section 16 did not impose an absolute prohibition on works lawfully authorised under section 15. Section 18 did not authorise the works.
7. The defendant’s decision was lawful and rational. The claim was dismissed.

First-instance judicial review. No earlier decision was stated in the judgment.