Sch 7 para 4
If the project is of a type mentioned in— (a) Annex I to the Directive; or (b) Annex II to the Directive and the Secretary of State considers that it would be likely to have a significant effect on the environment, the Secretary of State shall determine that an environmental impact assessment is required unless the proposed works comprise or form part of a project serving national defence as its sole purpose, or comprise a project having the response to a civil emergency as its sole purpose, and he considers that the carrying out of an environmental impact assessment of the works would have an adverse effect on that purpose.