He’s known as the sparkling mixologist, knocking up cocktails at moment’s notice and putting  nervous singletons at their ease as they embark on a first date in front of the TV cameras.

But few viewers of Channel 4’s First Dates would have been aware when watching Merlin Griffiths in the latest series of the show, that he was undergoing chemotherapy while filming.

Diagnosed with stage 3 bowel cancer last year, Griffiths, who had an operation to remove a tumour in April, told Sky News: “The last time we were we were working in the First Dates restaurant, I was undergoing chemotherapy and the team were fantastically accommodating.

“Tiredness was one of the really big side effects, I was getting a lot of fatigue. So, there was an allowance made so I could step away from the bar at regular points and have a small bite and get some rest in between seeing our beautiful daters.

“Likewise, as soon as we finished, I was straight off into the intravenous part of chemo … And that would really hammer me around. But that was ok because we had a break in running the restaurant at that point and then a few days later it was back in, and you’re ready to go again.”

Despite the demanding nature of TV schedules, Griffiths insists he’s nothing special in working through his illness, saying: “People manage full family lives, you know, several children, childcare and work and still go for chemo and everything else. You find ways of making it work because what else are you going to do? You’re trying to live.”

The fourth most common cancer in the UK, one in 15 men and one in 18 women will be diagnosed with bowel cancer during their lifetime.

But, while bowel cancer is the nation’s second biggest cancer killer, it’s very treatable when it is caught early.

Stars like Griffiths and the late Dame Deborah James have played a large part in bringing bowel cancer into the public consciousness.

But keeping the illness under wraps is an instinct Griffiths understands: “Initially I wanted to just keep it completely to myself and my immediate family… just to get my head around it… But then it was a case of, huge bits of my life are going to change and somebody might notice. Friends are going to go, ‘Why aren’t you coming out?’

“So, I just thought, you know what? After a conversation with my family, I might as well do something constructive with all this… I think it’s important to use this for good.”

Now in its nineteenth series, Griffiths has been part of the First Dates since it first aired in 2013.

Using his TV familiarity as a platform, he’s been frank about both his illness its treatments, the reality of which he’s described in social media posts as “long, and often painful and ugly”.

Unstoppably upbeat, he can’t resist joking about some of the less dignified treatments, saying: “My first thoughts on colonoscopy was that if I’d been kidnapped by aliens, at least they’d have the good manners to wipe my memory! But no, in reality it wasn’t actually that bad. And that’s why we shouldn’t be afraid to talk about it.”

He knows it’s not an easy subject to broach: “The tendency is to shy away from a lot of these things, especially because they’re sort of like embarrassing and stuff we don’t genuinely talk about”.

He even admits he initially put off seeking treatment himself: “It’s very easy for us to push stuff to the side, isn’t it? You can rationalise it and you justify it. I rationalised it myself.

“I was late to get checked in all fairness, and I should have made investigations sooner. I’m under 50, so I don’t come into the routine screening. So, the onus is on me as the patient to look after myself.”

His symptoms started with pain in his abdomen and radical changes to his bowel movements.

Other symptoms can include bleeding from your bottom and/or blood in your poo, unexplained weight loss and extreme tiredness for no obvious reason.

The NHS offers bowel cancer screenings to all adults aged 50 and over in Scotland, and that will soon be rolled out across England and Wales too (currently in parts of England and Wales people are not offered screenings until they are 60). Those in Northern Ireland are offered screenings from 60. Screenings are then offered every two years until the age of 75.

But Griffiths says searching symptoms randomly online can be unhelpful, labelling “medical Google” as “an absolute hellhole”. He says websites including the main charity pages including Bowel Cancer UK and the NHS have been invaluable to him on his cancer journey.

And he says he couldn’t have got through it all without the help of his family – his wife and daughter – and of course his First Dates family too.

“They’ve been absolutely awesome. I speak to Fred regularly and I chat with Cici [Coleman] regularly. They’ve both been really good and it’s been lovely to have their support. I chat with people that work behind the scenes on the show on a regular basis as well.”

Plus, he says the French maître d’hôtel Fred Sirieix who leads the team is as nice as he seems on camera.

“Fred’s Hilarious. He’s a live one… What you see is what you get with Fred. And it’s a wonderfully refreshing thing to find in someone. He’s cheery, he’s happy, he’s honest and he’s overwhelmingly positive about just about everything.”

Away from his gruelling treatments, Griffiths has at least had a little luxury travel to enjoy, albeit on a work trip for yet more filming.

Testament to the success of First Dates, its spinoff series – First Dates Hotel – is filmed in the four-star Aquapetra Resort and Spa in Campania southern Italy. The show is currently in its seventh series.

As Channel 4’s longest running dating show, First Dates has been matching singletons for nearly 10 years and has at least five weddings and three babies to its name. So, what’s the secret of its success?

Griffiths says it’s all down human nature – and a bit of forward planning: “Love is eternal, isn’t it? It’s not going anywhere. And people have infinite variety… When you put those two things together – a timeless emotion and a timeless base need – with the wonderful variety of people, it’s a recipe for success, especially when you actively look to make it happen.

“A lot of work goes into to matchmaking our daters as well, and that for me is one of the key things behind it. There’s a genuine desire from everyone who works at the restaurant to make it work, and that’s important.”

First Dates Hotel airs on Tuesday evenings on Channel 4.

Stay on Track is a campaign with Merlin Griffiths and Matt Dawson, in partnership with Norgine and Bowel Cancer UK, which aims to raise awareness of bowel cancer and the importance of screening, testing and early diagnosis. For more information: www.bowelcanceruk.org.uk