I was talking to a guy from one of the game angling clubs last week, who is involved with the environment agency. He gave me the number for this 24 hour hotline, if you spot anyone taking salmon or sea trout illegally, or undersize fish, or if you have any concerns about the legality of any netting operations or trawling, give them a ring on 0800807060.
Apparently they are not aware of any problems in this area, because none have been reported to them!