The Men Behaving Badly star is an experienced diver and was filming scenes for Clunes: Islands Of Britain when he had a panic attack and suffered breathing difficulties.
Martin told The Daily Record: “Those were the worst moments of my life – I knew I had to try to breathe normally but I was panicking and all I wanted to do was cry.”
The 47-year-old actor was exploring the wreckage of the John Strachan steamboat, which sank near Islay in 1917 after hitting a rock.
He continued: “Diving on the wreck was just horrible. It was scary. It does look very ghostly. I had only ever dived in warm water.
“I was scared about snagging my diving gear on something and getting trapped down there. But I started having trouble with my mask and it was making me panic. I just couldn’t stop my breathing from panicking.
“Your instinct is to get back to the surface as fast as you can, which is the worst thing you can do because you get the bends. But luckily, there was somebody on hand and they very slowly pulled me up.
“It was ghastly. I was going to dive in the Maldives when we were on holiday, but I didn’t – I just snorkelled.
“I am sure I will dive again. But I’ll never dive in British waters again.”
:: Martin Clunes: Islands Of Britain begins on ITV1 on Sunday May 3 at 9pm.