Devizes grandad Malcolm Humphreys has caused a splash in Thailand by becoming the first person ever to swim the five miles from the Royal Varuna Yacht Club to Koh Lan island.

Mr Humphreys, 75, from Drews Park, Devizes, last week fulfilled a promise he made to himself to swim the strait when he and his wife Norma became members of the yacht club 13 years ago.

He said: “It had never been done before but it looked so inviting. Gareth Owen, a former world champion catamaran sailor, became my mentor and it was his encouragement as much as anything that got me through it.”

The stretch of water between the yacht club and Koh Lan looks deceptively tranquil but it hides treacherous tidal currents and heavy crosswinds.

Mr Humphreys said: “I had a window of three hours to complete the swim before the next tide came through and I did it in two hours and 59 minutes.”

One of his fellow club members, Bud Rockey, attempted to swim with him but had to give up after about ten minutes because the swell of the waves was making him seasick.

Mr Humphreys completed the 4.24 nautical miles, or 7.85 kilometres, at an average speed of 2.66 kilometres an hour. Although no TV cameras were around at the time, when the news got out the Thai media went wild.

Mr Humphreys said: “The club organised a presentation evening for me and hundreds of people turned up. The TV cameras were there too and lots of complimentary things were said about me.

“People are now talking about swimming out to the island as a challenge they have to take up, so I have achieved something at least.”

The yacht club arranged for Mr Humphreys to be accompanied by two motor boats on his swim to protect him from other vessels, though there was always a risk from jelly fish, which are rife in the area. He came through without a single sting.

It is not the first marathon swim the grandfather to four has undertaken. At the tender age of 70 he swam two miles at the Isle of Wight to raise money for an Alzheimer’s charity.

His wife Norma said: “I think it’s absolutely fantastic. At 75, a lot of people are prepared to sit down and put their feet up.”

Mr Humphreys swims several thousand metres a week and belongs to the Devizes Masters swimming club.