The first sign that something was wrong with Emilian Gebrev was an itchy, bloodshot eye after a dinner in April 2015. The next day he had strange visions of flashing lasers, followed by uncontrollable vomiting. As friends rushed him to hospital, everything went black and he slipped into a coma.

Now, nearly four years after the Bulgarian arms dealer was on the verge of death after a suspected poisoning, British investigators are in Sofia to determine whether the incident could be linked to the 2018 poisoning of Sergei Skripal and his daughter Yulia with novichok in Salisbury.

The key link in the two cases is the alleged presence of a suspected agent of Russia’s GRU military intelligence using the alias “Sergey Fedotov” in both countries at the time of the incidents. The investigative website Bellingcat, which earlier identified GRU operatives Alexander Mishkin and Anatoliy Chepiga as suspects in the Salisbury attack, has said Fedotov is Denis Sergeyev, a high-ranking GRU officer and a graduate of Russia’s Military Diplomatic Academy.

Travel records show the man Bellingcat identified as Sergeev visited Bulgaria in April 2015 and was present in the country during the time Gebrev went into a coma.

Gebrev, a 65-year-old Bulgarian arms dealer, told the story of his 2015 poisoning during a series of meetings with the Guardian in Sofia. He said he was certain he was poisoned but he has no idea how he could have been a target for the GRU.

“It doesn’t make sense. If some GRU agent was here or not, I don’t know. But I almost died,” he said.

Gebrev said he did not notice anything suspicious in the hours and days leading up to the moment he fell ill, but also said that as his wife had died from cancer the previous month, he was not paying much attention to anything.

On 27 April, he said, he was “working like a cockroach” in the office and ate neither breakfast nor lunch. He then went for dinner with two longstanding Polish business contacts at an upmarket Sofia restaurant, where he ordered fish. When he got home that night, his eye started itching.

The next morning, his driver bought him some eye drops, but the itching got worse. He still wanted to make a business dinner that evening, however, with some different Polish contacts as well as two Russians. He was evasive about their identities, but said he had provided the names to prosecutors and that all the people were longstanding contacts who could not have been involved.

During the dinner, strange things began happening to his vision, and then the vomiting started and he swiftly deteriorated.

After he came round, Gebrev was informed that his son and a director of one of his manufacturing companies had also been poisoned and fallen into comas. The Bulgarian hospital was unable to do sophisticated tests, so Gebrev ordered testing from a Finnish laboratory, which suggested he had been poisoned by an organophosphate.

The former defence minister Boyko Noev, a close friend of Gebrev, was sceptical that Gebrev could have been a target for the GRU, but did say that Russia for many years had been attempting to gain control over licences in the Bulgarian defence industry. “Russia wants to strike arms deals in Africa and Asia, where Gebrev always beats them,” he said.

Gebrev believes the attempt to eliminate him could be related to his plans to acquire a stake in the Dunarit arms factory in the city of Ruse, on the border with Romania. “This was when the problems started. Somebody was not so satisfied,” he said. Others have suggested that an internal Bulgarian dispute could be behind it, with Gebrev’s domestic enemies seeking Russian help.

He said he had done no business with Russia, and had not or worked with Russian partners or middlemen. He had some contracts with Ukraine, but insisted they were “peanuts, small amounts, low tech”.

Bulgarian prosecutors dropped their investigation due to a lack of leads, but Gebrev approached them again a few months after the Salisbury attack, wondering about similarities with the poisoning of the Skripals.

“When it happened I didn’t even think about it, but then in October I was talking to a friend about it and I suddenly wondered,” he said.

The potential Skripal link appears to have moved Bulgarian authorities to act.

“We were immediately in touch with our British partners through all legal channels,” Boyko Borisov, Bulgaria’s prime minister, told the Guardian. Gebrev said he had a quick meeting with a Bulgarian prosecutor last week which lasted “15 or 20 minutes”, but otherwise has not been contacted by authorities.

Noev said he believed there had been a lack of interest in the case. “My suspicion is that it was a deliberate cover-up. Bulgaria and some of Bulgaria’s main institutions do not want this case to be investigated further,” he said.

Bulgaria was once the Soviet Union’s closest ally in Europe and unlike other EU and Nato members did not expel Russian diplomats in response to the Salisbury poisoning. It recalled its ambassador to Moscow for consultations for a short period of time, but stressed that more evidence was needed for further action.

Trying to remember the sequence of events around the suspected poisoning is challenging for Gebrev, who is often hazy on details. Shown a photograph of the man Bellingcat identified as Sergeyev, Gebrev said he did not recognise him.

Hamish de Bretton-Gordon, a chemical weapons expert, said the Finnish lab results were inconclusive, but suggested that Gebrev was probably poisoned with a pesticide rather than a weapons-grade agent. “The toxicity of a pesticide compared to a nerve agent is minimal but still easily enough to cause death.”

An added oddity is that Gebrev claims he, his son and his business partner did not cross paths in the days running up to his poisoning. The other two men fell ill three days after him. “We sat down together and tried to work out where we could have got it from, but couldn’t,” he said.