He was among 1,000 surfers taking part in a competition on the Severn estuary, which has the second highest tidal range in the world.
The race last Thursday began at Newnham-on-Severn, where the four-foot wave was at its peak, and by the time it had travelled two miles inland, all the competitors - including professionals from the United States and Australia - had come off their boards except Mr King.
"It was the most incredible experience of my life," Mr King said yesterday. "Hundreds of surfers were falling off their boards every minute, but I managed to stay on and keep my nerve. As time went on, people kept shouting encouragement to me from the bank, so I knew then that I had a chance to break the record.
"One hour 17 minutes went by until the wave broke and I was able to crawl out to the bank and find out exactly how far I'd gone. I jumped for joy when I was told I was a record-breaker."
Mr King has been riding with friends from the Severn Bore Surfers Club for more than 20 years. They ride a tidal phenomenon - known as a bore - which occurs when a rush of water is funnelled into the 30-mile estuary's narrow channel.
It starts at the mouth of the estuary at Avonmouth near Bristol and reaches as far inland as Gloucester. The phenomenon occurs 12 times a year during the spring and autumn equinox, when a wave is formed every morning for between two or three days.
Mr King said his experience of the bore kept him on his feet: "[It] was very tiring and mentally draining... but it was worth every second of pain."
The National director of the British Surfing Association, Karen Walton, said the "remarkable sporting feat" was witnessed by a BSA official who confirmed it was a new world record.
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