A coroner's inquest opens in London on Monday into the mysterious sinking of a French fishing trawler 17 years ago, which the victims' families blame on a submarine.

French courts spent years investigating the sinking of the Bugaled Breizh in international waters off Cornwall, southwest England, on January 15, 2004.

But there has never been a full explanation about what happened.

The ship's crew of five French nationals -- Yves Gloaguen, Pascal Le Floch, Georges Lemetayer, Patrick Gloaguen, and Eric Guillamet -- all perished in the sinking.

Judge Nigel Lickley will hold inquests into the deaths of Yves Gloaguen and Le Floch, whose bodies were found by UK search and rescue.

Over three weeks, the judge will hear around 40 witness statements from seamen, rescuers, maritime experts, submarine commanders and the victims' families.

Inquests are held in England and Wales in the event of a sudden or unexplained death.

The hearings establish the causes and circumstances on the balance of probability. They do not determine criminal or civil liability, but set out facts in the public interest.

In particularly sensitive or important cases, a judge can be appointed to oversee proceedings.

'Great hope'

The victims' families have insisted from the start that either a British or US submarine got caught in the boat's nets and dragged it down.

British and NATO submarines were in the area for military exercises at the time.

Operating out of the Finistere region of northwest France, the Bugaled Breizh -- "Children of Brittany" in the local Breton language -- sunk in less than a minute.

Weather was fairly good at the time.

Patrick Gloaguen's body was discovered in the wreck during salvage operations but those of Lemetayer and Guillamet have never been found.

The men's families have long awaited the UK hearing, which they hope will endorse their version of events, after lengthy proceedings in France were inconclusive.

Lawyer Dominique Tricaud, who represents the children of Lemetayer, told AFP: "This gives us very great hope. The London court is dedicating three weeks of hearings to this case.

"It will get to the bottom of things and the families, who have never given up, have never had such great hope.

"The families think that the (British submarine) HMS Turbulent was responsible for the sinking and are waiting for the trial to prove it.

"They're not out for revenge but can't grieve on a state lie."

'Full and fair' probe

The former commander of HMS Turbulent, Captain Andrew Coles, will give evidence to the inquest on October 12 about the vessel's location on the day the Bugaled Breizh went down.

A senior officer from the Dutch navy's Dolfijn submarine, which is known to have been in the area at the time as part of a NATO training exercise, will also give evidence.

Britain's Ministry of Defence and the Royal Navy have both denied claims that one of its submarines was involved in the sinking.

In 2006, the French Marine Accident Bureau concluded that the sinking was an accident, most likely caused by one of the boat's trawler net cables snagging on the seafloor.

Other scenarios, such as a collision with a freighter, have been ruled out.

The French probe ended after an appeal in June 2016, when it failed to prove definitively whether the trawler sank in a sea accident or whether a submarine hooked onto one of its cables.

The inquest into Yves Gloaguen and Pascal Le Floch's deaths began in Cornwall in 2020 but was adjourned due to Covid-19 restrictions and transferred to London.

At a March hearing, judge Lickley spoke to the fishermen's families via video link, promising to "carry out a full, rigorous and fair investigation".

Lickley also said the inquest had been informed by the Ministry of Defence that "no non-allied submarines" were present at the time of the sinking.