The body of a 23-year-old bar manager was found on a deserted shoreline in the Isles of Scilly after a rowdy party on a tiny, exclusive island, an inquest has heard.

Relatives of Josh Clayton alleged the staff party on the privately run island of Tresco included drug-taking, heavy drinking, sexual harassment and assaults.

They questioned why such an event was taking place on an island that prides itself on being crime-free and criticised the police for the way they investigated his death.

Clayton, from Taunton, Somerset, disappeared after a party hosted by Tristan Dorrien-Smith, whose family leases the island from the Duchy of Cornwall.

He was reported missing on 13 September 2015, when he failed to turn up for work on the island, about 28 miles (45km) off the south-west tip of mainland Britain. Clayton’s body was found 10 days later after being spotted by a French yachtsman on rocks on an uninhabited Scilly island called Tean.

The inquest was suspended in 2017 after fresh claims emerged of a row at the party from Leroy Thomas, who said he saw Clayton “arguing with two foreign workers over a pushbike” before running off.

Det Chief Supt Steve Parker, of Devon and Cornwall police, told the inquest jury on Monday there was no evidence of a third party being involved in Clayton’s death or of him killing himself. He said he did not appear to have suffered any injuries or drowned and the cause of death could not be ascertained.

Parker also said Clayton would not have gone swimming fully clothed and with a rucksack, which was found around his head when his body was recovered.

Asked about some of the incidents that allegedly took place at the party, Parker said: “Clearly it was unacceptable behaviour. There were a lot of incidents unusually that night, it was not an average Saturday night on Tresco.”

Parker apologised that the postmortem was delayed, saying: “It was unacceptable and a mistake.”

The family also claimed that Clayton’s clothes, including a bloodstained T-shirt, were destroyed by police and not forensically examined.

Parker said Thomas, a painter and decorator, had given five separate accounts, each slightly different, about the night.

Thomas had claimed he saw Clayton outside the venue where the party was being held, in an agricultural building called the Shed. Thomas said Clayton was arguing with two eastern European men over a bicycle. He claimed Josh threw down the bike and shouted: ‘I have had enough. I want to kill myself.” Thomas then claimed Josh ran off towards a thicket.

The detective said police tried to trace the foreign workers but added: “We could not find anyone who had knowledge of the incident as described.”

Jurors were told witnesses described Thomas as being involved in an altercation and as upsetting women at the party.

In his statement to police,Dorrien-Smith said Thomas had been “a bit of a nuisance” but that he was unaware of claims that he [Thomas] had been behaving inappropriately.

When the search was launched, some of Clayton’s possessions were found on a track – and a damaged pushbike was found nearby.

Toxicology tests showed Clayton was 2.5 times the legal drink-drive limit. Other partygoers said he had taken some “drags” on a cannabis joint but there was no evidence of drugs in his system.

The inquest continues.