The distinction between Irish ships and relevant Irish ships was not required when the 1999 Act was made. The requirement to prepare plans, etc., in respect of oil was already in place through SI 44 of 1994, which was made under the 1991 Act. The extension of this requirement to hazardous and noxious substances in the protocol has meant that the Bill needed to provide for Irish ships above a certain threshold to prepare plans, etc. As regards HNS, the Office of the Parliamentary Counsel, when drafting the Bill, recommended that the requirement for relevant Irish ships in respect of both oil and HNS should be set out in this legislation.