‘Reefs’ are listed under Annex I of the Habitats Directive as a marine habitat to be protected by the designation of Special Areas of Conservation. Crucially for the implementation of the Directive, the distinction between what is considered as ‘reef’ and what is not is imprecise, particularly in relation to colonies of the tube-building polychaete Sabellaria spinulosa. Guidelines are proposed for the implementation of the Habitats Directive definition to provide a robust and transparent approach for the benefit of both regulators and offshore industry. Specifically, it is suggested that the conservation priority of a S. spinulosa aggregation could be determined using a scoring system based on a series of physical, biological and temporal characteristic reef features, weighted according to the perceived importance of each feature and augmented with a further score indicating the confidence in the feature score. Suggestions are given as to how these characteristics might be measured and scored, along with an example to illustrate the application of the approach.