Ross Kemp recalls moment he was "starved of oxygen" on Deep Sea Treasure Hunter

Despite his qualifications, Kemp was faced with a number of new challenges – not least during a dive at Plymouth Sound. In episode two of the new series, viewers will see the host struggle to breath when he stays under the water longer than recommended – with his oxygen running low, he experiences hypercapnia, an increase in blood carbon dioxide levels, due to inhaling too much CO_2.

"To work underwater is a challenge – that's where you've got to have an HSE [Health and Safety Executive] ticket and that's why it's hard to get one," Kemp told RadioTimes.com.

Recalling his tense moment under the water, he said: "You've been starved of oxygen, because you've been breathing in so much CO₂, so you can feel your lungs – the oxygen capillaries, the alveoli – filling up with oxygen. So that's a weird feeling."

Returning to his hotel in Plymouth, Kemp asked a member of the crew to stay in regular contact. "I laid on the bed and I said to the assistant cameraman, 'Make sure I don't fall asleep, ring me every hour just to make sure I don't fall asleep...'

"There was no chance of anything bad happening, you just breathe it [the carbon dioxide] out – basically over a 24 hour period, you're back to normal. But yeah, look, it's a hostile environment, water, and you got to treat it with a lot of respect."

Kemp's dives – and his on-camera pieces filmed underwater – had to be carefully choreographed beforehand. "It's like doing a pre-planned dance – or it's no different from doing a play."

Helping him to prepare before each excursion were a team including dive supervisor Neil Brock and maritime archaeologist Mallory Haas. "Me and Mallory, probably the most unlikely partnership you'd ever want – a marine archaeologist from America with an ex-soap actor," Kemp laughed.

"But yeah, we're a really close, bonded team – it really works and I think it comes over [on screen]."

The first episode of Deep Sea Treasure Hunter also marks a TV first, with Kemp being granted access to the site of the Mary Rose shipwreck, Henry VIII's flagship which sank in 1545, the precise cause of the sinking remaining unconfirmed to this day.

Personally recovering a piece of wood thought to be from the ship's bow was, said Kemp, "like shaking hands with a ghost".

"No one's seen this bit of wood since it sank 500 years ago. Someone could have been holding onto it as the ship sank... and here I am holding it. I'm the first person to touch it in that time – it’s shaking hands with ghosts, and I love it."

So what next? After a seven-year break from acting, Kemp has recently wrapped filming on the Channel 5 thriller Blindspot in which he'll play a police detective, but he's also keen to get back in the waters before too long.

"What I love about this series is I think it works on lots of different levels. It's got a good family entertainment vibe to it. There is an element of jeopardy to it, because you're working in a hostile environment and things do go wrong because the sea's unpredictable.

"It also makes history digestible. It's telling history in a very un-dry way – in fact, quite wet! But it's discovering history, You're on a little voyage.

"I honestly think – I would say this, wouldn't I? – but this is a better series than the first, even though the first was pretty good. It's whether there's an appetite from Sky History and from the audience for more. But there's still more to see."

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Ross Kemp: Deep Sea Treasure Hunter airs Mondays at 9pm from 10th April on Sky History – sign up for Sky TV here.

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