[Ammi]

Detectives are investigating the deaths of a couple whose bodies were found underwater in the swimming pool of an exclusive country house hotel.

The man and woman, who have not been named, were staying together at 14-century Down Hall in Hatfield Heath, Essex, on the same night a murder mystery party was due to take place

Their bodies were found at 7.35pm on Saturday in the spa area of the historic Italianate mansion.

Among the other functions being held, there was reportedly a murder mystery game and the real-life “unexplained” deaths were initially viewed as being part of a “fantastically realistic event” by revellers.

“It was only then that the police told us there had been a real incident and two people were dead,” one hotel guest told the Daily Mirror.

Staff dived into the water to save the man, aged in his 30s, and the woman in her 20s, but they could not be resuscitated. Both are believed to be from the London area.

Police said they had checked in together but it is not known whether they were among the groups celebrating at the hotel-conference centre. It was reported they were dressed in their swimming costumes.

The hotel itself advertises its Murder Mystery breaks which it claims offer visitors a “night of intrigue and suspense”.

Detectives are treating their deaths as unexplained. There is understood to be no evidence of foul play and investigations are continuing. A post-mortem examination is due to take place today. No one else is being sought in connection with the incident.

Chief Inspector Nick Lee said staff and emergency services had battled “valiantly” to save them. He said: “As part of the investigation we are trying to focus on what the relationship was between the victims.”

He added: “It’s a very busy hotel; there were a number of functions going on. At the moment we haven’t ascertained whether these individuals were part of any function.” Investigating officers from the Kent and Essex Serious Crime Directorate described the incident as “very unusual”.

Set in 110 acres of surrounding woods, parkland and gardens, near Bishop’s Stortford on the Hertfordshire and Essex border, the venue is a popular place for weddings and business meetings. In 2009 it played host to the wedding of the late-Big Brother star Jade Goody and her husband Jack Tweed.

The manager, Chris Falcus, said: “We are devastated by this tragic incident and our thoughts are with the families and friends of those concerned. We are co-operating fully with the police investigation.”

Louise Saunders, a guest, had spent two nights at the hotel celebrating a birthday. “We were going to use the pool about 5.30pm but decided against it as the pool was busy with families and children. I’m so glad now we didn’t,” she said.

Police and scene of crime experts spent all night and yesterday at the scene – a building separate to the rest of the 99-room hotel