“I kept shaking in the water and could only keep thinking – ‘I can withstand being immersed in iced water during exercise,’” he said.

“How can this be difficult for me? As long as I persist, I will definitely do it.”

Leung, 35, said the middle section of the marathon swim was easier because the tide helped him along.

But he hit difficulties in the final sprint to the finish line, when a sudden change meant the tide turned against him.

“It was as if I was swimming against the current,” Leung said. “Fortunately, the team kept cheering me on.”

He added that it had taken him about three hours to complete the final 7km.

Leung started from Donaghadee, in Northern Ireland’s County Down, and finished in Portpatrick in Dumfries and Galloway, Scotland.

He completed the swim in the early hours of Sunday, Hong Kong-time.

The North Channel is the longest and considered to be the most difficult of the Oceans Seven marathon swimming challenge because of the chilly North Atlantic, rapid tide changes and the presence of lion’s mane jellyfish – one of the largest species of the creature known.

The Oceans Seven challenge includes some of the toughest channel swims in the world and is seen as the open water swimming equivalent of mountaineering’s Seven Summits.

Leung also used his herculean effort to raise money for good causes.

He had raised about HK$20,000 for the Child Development Initiative Alliance, an NGO dedicated to the support of underprivileged young people through education, employment opportunities and job training, before he left for Scotland in June.

Leung, who works in property development, earlier told the Post he swam for 100 days in a row to prepare for the ordeal, often for three hours before he headed to work for 9am.

His preparation also included completion of a 10-hour swim in waters of about 13 degrees, which was what he expected to experience in the Irish Sea.

Leung, who earlier studied and then worked in the United States, was a keen competitive swimmer when he was younger.

A setback in his US business during the Covid-19 pandemic led him to return to Hong Kong in 2021, where a friend introduced him to open water swimming – which reignited his passion for the water.

Leung said his friend had died a year later and the tragedy had inspired him to “act and not wait”.

He has taken part in several competitions since then and picked up a number of accolades.

He and three other Hongkongers formed a relay team to swim across Scotland’s Loch Ness, the second-largest body of water in the country, the first Hongkongers to do so.

The team also raised HK$11,600 for the Community Chest, a non-profit organisation for the underprivileged.