SYDNEY (AFP) - A 70-year-old Australian grandfather has become the oldest person to swim the English Channel, celebrating his feat by having a couple of beers "for medicinal purposes".

Cyril Baldock, from Bondi in Sydney's eastern suburbs, said the beer tasted better than the sea water he swallowed during the record-breaking swim from England to France on Wednesday, which made him "pretty crook", or unwell.

Baldock, aged 70 years and nine months, took 12 hours and 45 minutes to swim from Dover to Cap Gris-Nez - a straight line distance of 34 kilometres (21 miles) - beating the previous record set by British man Roger Allsopp, who was five months younger, in 2011.

"I'm having a couple of beers for medicinal purposes only, to make myself sleep," Baldock told Australian Associated Press after he completed the swim in only a cap, goggles and trunks as Channel swimming rules dictate.

"Around the 10-hour mark I had a bad half-hour and was starting to worry a bit," he said. "The arms were really sore, and I didn't seem to be making much ground, but I kicked on again."

Baldock, who first swam the English Channel in 1985, becoming the fifth Australian to complete the course, said he wanted to break the record for his mentor and coach Des Renford, who wanted to make the swim but suffered a heart attack.

"Des wanted to have a crack at that but obviously it was never going to be," Baldock told the Australian Broadcasting Corporation. "I told Des that when I got to that age I'd have a go at it. But little did I know over that 30-year period the oldest went up 10 years, so I had to wait a while."

Baldock's feat, which was recognised by Guinness World Records, may not stand for long, with Australian grandmother Irene Keel, 73, also set to attempt the crossing this week.