Article 6 of the Habitats Directive (Council Directive 92/43/EC on the conservation of natural habitats of wild fauna and flora) requires that any plan or project (either individually or in combination with other plans or projects) which is not directly connected with or necessary to the management of a special area of conservation but is likely to have a significant effect on such an area be subject to an appropriate assessment.
Where the above test is satisfied, the Offshore Petroleum Activities (Conservation of Habitats) Regulations 2001 (as amended) set out the matters in respect of which I must carry out an appropriate assessment e.g. before granting a Petroleum Act licence, a seismic survey consent, a consent issued under a Petroleum Act licence, etc..
I am also guided in the selection of plans or projects for assessment by information and guidance such as that provided by the European Commission; "Assessment of plans and projects significantly affecting Natura 2000 sites" and that provided by statutory conservation agencies such as the JNCC.