To simplify administration all UK licences will be issued on behalf of the four fishing administrations by the Single Issuing Authority (SIA) operated by the Marine Management Organisation.
Further details of the SIA and their operation can be found here: (link text Single Issuing Authority) (https://www.gov.uk/government/publications/united-kingdom-single-issuing-authority-uksia)
All fishing vessels in UK waters must comply with British sea fisheries legislation. In addition to national legislation you must comply with the legislation of the Devolved Administrations when operating in their adjacent waters.
Vessels operating in the Northern Ireland Zone, that is the waters within the British territorial limits adjacent to Northern Ireland, (as defined in The Adjacent Waters Boundaries (Northern Ireland) Order 2002, must comply with Northern Ireland legislation.
A list of the specific Northern Ireland legislation in force can be found here Northern Ireland legislation applicable to non UK vessels fishing in NI waters