A promising law student who drowned in the Thames had been drinking to celebrate the end of 28 days of abstinence, an inquest heard.

Niall Pawsey, 20, disappeared under the water just 5m from the Middlesex side after trying to swim across the river in Kingston on Thursday afternoon, April 28.

Daniel Bellows, who studied law at Kingston University with Mr Pawsey, said his friend had been drinking after winning a bet he could stay sober for a month.

He said they were thrown out of the Mill pub after a glass smashed.

Ryan Ridley, who was at a table next to Mr Pawsey, criticised the pub for telling people, that he said were clearly drunk, to leave by back doors that opened onto the river.

Mr Bellows said conversation turned to an old joke about swimming across the river, and Mr Pawsey stripped to his underwear and dived in.

He said: “We thought he had got over to the other side. We did not realise he had gone under until everyone started panicking on our side of the bank.”

Mr Bellows said he had dropped out of university since the tragedy, but Mr Pawsey’s mother Patricia urged him to “go back to university and build a life for himself”.

Rowing instructor Andrew Beard, who was training four school boys on the Thames at the time of the tragedy, was near the Kingston side of the river when he spotted Mr Pawsey swimming.

He told the inquest he initially believed Mr Pawsey was making good progress swimming on his front and back.

He said he rowed towards him in case he got in trouble, and threw a buoy when he stopped swimming, but Mr Pawsey made no effort to grab it and started to go under.

Mr Beard said he jumped in the water and spent five minutes trying to find Mr Pawsey, while desperately shouting at people on the other side to call the emergency services.

He said: “There will not be another day of my life when I don’t wish I had gone in five seconds earlier.”

A police helicopter scoured the area, but Mr Pawsey’s body was found three days later, 10m from the riverbank.

A post-mortem showed he had 319mg of alcohol per 100ml of blood, a level coroner Alice Thompson had proved fatal to some people.

Recording a verdict of death by misadventure on Tuesday, September 6, she said: “It was a risk taken by a young man in high spirits enjoying himself, with a very high price for him and the family left to deal with this.”