A bartender has been arrested over a deadly cocktail he allegedly served to a British woman and her fiance in Vietnam.

Le Tan Gia, 45, was detained by police in Hoi An, where Greta Marie Otteson, 33, and Els Arno Quinton, 36, from South Africa were found dead on December 26 last year.

Police confirmed that both victims died from methanol poisoning. The suspect was charged with 'violating food safety regulations'.

A police spokesman said: 'The Criminal Investigation Police Department of Quang Nam Province has arrested Le Tan Gia, of Cam Nam Ward, Hoi An, on charges of violating food safety regulations.

'The prosecution of the defendant will continue, based on the evidence that he served the victims methanol drinks that caused their deaths.

'Currently, the case is being investigated and handled by the police force in accordance with the law.'

Officers said that Le Tan Gia served the couple at a restaurant at around 3:30 pm. He allegedly used 70 per cent medical alcohol - intended only for disinfection - to prepare two bottles of the lemon liquor Limoncello

Officers said the suspect mixed the alcohol with filtered water, lemon peels, and white sugar before serving it to the tourists.

But shortly after drinking the solution, Greta and Els suffered severe methanol poisoning.

They were discovered dead by shocked resort staff in separate rooms at the Silverbell villa in Hoi An Town in central Quang Nam province.

Greta was said to have been lying in her bed lifeless in room 101. Officers then barged into Arno's locked room and also found him dead.

A Quang Nam Provincial Police spokesman said: 'There were no signs of ransacking at the scene. The victims' belongings and phones were untouched.'

Police said there were also no signs of scratches or physical trauma inflicted on the bodies. They collected several empty liquor bottles in the room for further analysis.

Arnold's friend Dayle Visser wrote online: 'Rest in peace my brother. Thank you for always being the fierce friend you were. You saved me many a time.

'You were real and lived life harder than most people could ever dream of. I love you and I will always miss you.'

Local media reported that Greta and Arno had been staying together in the villa since July 4. The pair are understood to have been engaged this December.

Travel lover Greta had previously lived in Dubai and backpacked around different countries in Asia before settling more recently in Vietnam.

She was a digital strategist who ran a social media and content marketing agency called Not Sorry Socials. While Arno was a barista, musician, and streamer.

Police said that the investigation into the deaths is ongoing.