Nine years after five Breton fishermen died when their trawler sank off the English coast, French authorities have finally ruled out the possibility of a British submarine being responsible.

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Two expert reports published on Friday dismiss a theory that the Royal Navy's HMS Turbulent, or any other submarine, could have got caught up in the trawler's cables and dragged it down.

The families of the men who died on board the Bugaled Breizh have long suspected that a submarine was responsible for the unexplained January 15, 2004 sinking off Lizard Point in the English Channel.

Traces of titanium found on the cables after the trawler was salvaged fuelled their suspicions and sustained a legal probe that continued despite the French Marine Accident Bureau concluding in 2007 that the sinking was most likely caused by a cable snagging on the sea floor.

The families suspected that the titanium could have come from the paintwork of a submarine.

That theory was dismissed however in the forensic report commissioned by the Nantes prosecutor.

"It concluded that the miniscule traces of titanium found on the cables of the Bugaled were not indicative of the involvement of a submarine," the prosecutor, Brigitte Lamy, said in a statement.

A second report, carried out by a naval expert who was specifically asked to look into the Turbulent's movements, found that the British sub was definitely in port on the day of the sinking, the prosecutor said.