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A Cambridge student who drowned on a family holiday in Malta last August had been warned not to swim in a underwater tunnel as a 'challenge' the Daily Mail reported.

Marcus Hughes-Hallett, 20 ignored the warning but failed to emerge from the water off Comino. He was found 20 minutes later, but it was too late.

Marcus, a maths student at Queens College, was on an adventure holiday with his parents David and Kristen, and younger brother, Christian.

Mrs Hughes-Hallett said the warning was made by a boat skipper, saying swimming through cave tunnels was dangerous.

'I heard David shout that Marcus had swum through (the tunnel) and he shouted at me to go through to the dark cave and see him come up the other side,' said Mrs Hughes-Hallett.

'It was about 10 metres underwater.'

Mrs Hughes-Hallett said that prior to diving into the tunnel, Marcus told his father what he had planned.

'He just said to his Dad "I’m thinking of going back underwater," and David said, "don’t do it",' she said.

'He said he had already done it the other way and it was really easy.

'He was a very confident swimmer and had done it one way.'

However, this time Marcus failed to reappear on the other side of the tunnel, prompting panic among the other family members.

'I think I just froze a bit, I didn’t know what to do,' said Mrs Hughes Hallett.

'My youngest son ran back to the boat.

'I don’t know what happened. Going from the light cave to the dark cave was obviously very different to going the other way.

A Maltese diving expert said that any attempt to skin dive within the cave tunnels was a 'very dangerous activity'.

Barry Nolan runs Activity Travel, the company that organised the family’s trip and conducted an investigation following Marcus’s death.

'We do not believe anything was wrong with the procedure that day,' he said.

'That was the inevitable conclusion we reached.'

However, Mr Nolan said that holidaymakers were now expressly told they should not swim in the underwater tunnels.

Assistant Surrey Coroner Michael Burgess recorded a verdict of accidental death.