New guidance has been issued to Royal Navy submarines operating in the Irish Sea.
The move comes after a Co Down fishing boat The Karen was almost dragged underwater after its nets were snagged on a submarine last April.
At the time the Ministry for Defence said the incident did not involve any of its vessels.
However, it later admitted that in fact one of its submarines had been involved and claimed that it had failed to identify the Karen as a fishing boat.
South Down MP Maragert Ritchie last night said she has been told by British armed forces minister Penny Mordaunt that new guidance has been issued to senior officers.
"According to the Minister for the Armed Forces the process by which a vessel is classified has been reinforced, using even stricter criteria to prevent incorrect assumptions being made by the submarine," she said.
"If a vessel’s identification cannot be definitively established, the Commanding Officer must assume that it is a fishing vessel with nets in the water and behave accordingly.
"This instruction now informs the training given to future Commanding Officers."
Ms Ritchie said she has also been assured that the Royal Navy’s reporting procedures have been reviewed to allow it to confirm more quickly if one of its submarines has been involved in an incident.
"I hope that further such incidents involving the Royal Navy and other such vessels will not happen again," she said.
"Fishing effort must be allowed to take place unhindered and without obstacles being put in the way of fishermen and the fishing industry.
"I will continue to pursue and review this issue both with the fishing industry and the Ministry of Defence."
