Liz Saville's husband Tim, 61, died on a 106m dive to the sister ship of Britannic in September 2019 off the island of Kea. Fellow rebreather diver Dr Vincent Hong, 53, died on the same trip, two days previously, when he got into difficulties ascending from a wreck at 63 metres.

An open verdict was recorded after an inquest last week, however coroner Professor Paul Marks didn't rule out carbon monoxide poisoning as a potential cause. The odourless, invisible gas is produced when fossil fuels burn without enough oxygen, is most often associated with faulty domestic boilers.

But diving cylinders can become contaminated; while people on board boats, including divers waiting to go into the water can breathe in engine or exhaust fumes.

Mrs Saville, who ran Robin Hood diving club with her husband, a co-director at Bronte Water Coolers, at Honley, had to hire a solicitor just to see the police report into her husband's death.

She said: "It was emotional, just horrific, when the Foreign Office said you won't be able to get a police report if you haven't a lawyer, that's the way they operate.

"It took six months to and when it finally came through I couldn't believe what I was reading."

An autopsy carried out in Greece, and a second in the UK came to different conclusions.

The UK report found no features of drowning or coronary heart disease, but did find raised levels of carbon monoxide in the bloodstream. The Greek authorities hadn't taken samples for the gas or tested the cylinders.

Mrs Saville said Dr Hong's tanks were empty when they were taken to the port authority in Kea. Her husband's were taken promptly, but not analysed by the police investigator: "It was only six months later when we got the police report that we put in motion an investigation to have them properly analysed. Tim's were clear of carbon monoxide - I think the most likely scenario is the boat engine.

"The initial post mortem hadn't tested for carbon monoxide which in two unexpected diver deaths is negligent in my opinion.

The Greek owner of dive company Kea Divers is due to stand trial in January in Athens for negligent manslaughter. Mrs Saville is unsure whether they will ever get to the bottom of the cause of her husband's death, but hopes that raising the issues will help ensure investigations are more thorough in future.

"I just feel as a family we were really left with no answers. I'm a diver myself and it could have been me or any of my friends and I would hate to think they would have to go through what we had just to get basic information." Mrs Saville said her research showed hundreds of cases a year, many involving pleasure craft on lakes in America.

She said: "I'm not out for a witch hunt or even looking for someone to blame, I just want basic things checking.”