Westcountry fishermen say they were attacked off the coast of France after fighting between rival boats broke out over quotas in prized fishing grounds.
About half a dozen fishing boats from Brixham were surrounded by 40 French boats in the Channel 20 miles north of the French coast where the fishermen say they were pelted with stones and attacked with flares.
Anton Bailey, from Brixham, said he was surrounded by boats while fishing legally in international waters off Le Harve, which had been previously been closed off to French boats. He said crew members pelted his boat with rocks, fired flares at the crew and even tried to ram him.
"I have never seen this before and I have been at sea 20 years," he added.
"They were shooting flares at other vessels, every underhanded thing you could think of.
"Then they threw rocks at us and tried to ram us."
Fishing groups in the region say the Government has failed to help secure adequate quotas and days at sea in a dispute over lucrative scallop beds.
The fishing minister is said to be "monitoring very closely" the situation, which has been described by Totnes MP Sarah Wollaston as "totally unacceptable".
Dr Wollaston added: "I have spoken to Richard Benyon about this and he is very concerned – if our trawlermen are fishing legally there is no way they should be subjected to threats.
"Scallopers are unhappy about quotas and days at sea but the worst way to resolve this is to use intimidation – we expect the French to investigate and take this very seriously indeed."
Jim Portus, from the South Western Fish Producers Organisation, said negotiations had broken down, leaving French boats with five times the potential catch from the area.
He said the French fleet outnumbered Britain with around 100 boats compared to 12, with British boats only receiving 36 days of available fishing in three months from October.
"We don't usually have antipathy like this and before this kicked off we were endeavouring to come to an agreement," he added.
"Negotiations have failed this year and Government departments have not been supportive in doing these deals.
"We need to get to the nearest productive scallop beds and these are where the aggravation is kicking off – France has got a hell of a lot more boats involved."
The Marine Management Organisation (MMO) detected the fracas using satellite monitoring system on Monday in the Bay de Seine.
Rod Henderson, head of coastal operations: at the MMO, said: "The MMO has the difficult balancing task of ensuring that fish stocks are not overfished and are managed throughout the year.
"The MMO is continuing high-level discussions with French counterparts to seek assurances that these issues will not recur."