A French woman with no government or port affiliations turned a vessel from Alderney away from a French port.
The Bailiwick boat skippered by Lewis Main was attempting to land at Cherbourg yesterday.
In a statement Deputy Neil Inder said:
"On 1 December the Bailiwick issued 40 fishing licences in accordance with the UK-EU Trade and Cooperation Agreement (TCA), with track records approved for three vessels where licences were not initially sought.
These licences were issued in accordance with the requirements of the TCA.
This has been welcomed by the European Commission and the French Government as well as by the Normandy authorities including the Normandy fishing committee.
There has been no official policy change on landing in EU designated ports but disruption from non-governmental sources cannot be ruled out.
Disruption caused by individuals is extremely disappointing, given our commitment to transparency in the processing of licences and our aim of providing stability to the fishing economy within our joint region."
French officials are said to have condemned the actions of the person concerned.

Prime Guernsey seafront location for sale
Woman (20) arrested on suspicion of attempted murder in Guernsey
Last day to register for Guernsey's upcoming by election
New citizen science project observing Guernsey dragonflies and damselflies
Channel Islands music school to hit global stage with Dubai launch
67,000 sickness days across the States of Guernsey last year
The Channel Islands are officially in meteorological drought
Islanders asked for views on body image and masculinity