He’s the quiet, controlled one who wowed the judges with precise technical bakes. At least, that’s the impression you probably have of the 2019 Great British Bake Off winner, David Atherton. Wrong. In person, he’s an adventurous extrovert with a hippy streak. “Most of my practices I did in my pants while eating pizza and watching RuPaul’s Drag Race. The person in the edit is not me,” he says. “At the end, it showed me singing to myself and dancing around, but actually I did that the whole way through. I am calm and methodical, but I’m not particularly reserved.”

Atherton’s triumph – he didn’t win a showstopper while the hotly tipped finalist Steph Blackwell was star baker four times – is all the more remarkable because he was a reserve applicant (as was his co-finalist Alice Fevronia), drafted in to replace a dropout just two weeks before the show began. Yet the 36-year-old health adviser is such an experienced and confident cook (“Ottolenghi is my absolute hero,” he says, and he is a big fan of baker Dan Lepard), he didn’t panic or even change any social plans. “The weekend before the show, I decided to cycle to Paris. It was good for my headspace.”

A fitness fanatic, he had made his stunning snake cake only once before the opening show. “My thought was that if you’ve tried something and it’s worked, don’t keep on practising it, because if you try it again and it doesn’t work, it’s just going to stress you out. A lot of Bake Off is your mental strength.”

He thought dessert week might be his undoing. “Sweet, fancy, fluffy desserts are not my thing. I like robust flavours and hearty bakes. I like breads. If I do a cake, I want it to be a carrot cake. If I do biscuits, I want them to be spicy.”

Judge Paul Hollywood wasn’t initially a fan of his flavours. “Paul has, I think, quite simple tastes. He likes really obvious flavours – chocolate and caramel and raspberry and white chocolate and lemon.” Yet Atherton won a handshake and is happy to return the compliment: “He’s very technical. I always agreed with their constructive criticisms. He was really helpful with tips. He must enjoy teaching because he’s really good at that.”

While all around him were dropping their creations or gasping as they ran out of time, the cheerful, unfazed Atherton always seemed to finish with a few moments to clean his workbench. Is he really this perfect – prissy even – in real life?

Not at all. “I’m not that clean and tidy. I don’t like showering. I never wear shoes. I’ve not washed my hair in more than 15 years. I didn’t go to a hairdresser until I was about 28. I think these things are healthy.

“I’m very hippy and outdoorsy. I love talking about my bowels and anything disgusting and medical.”

His Bake Off persona only shows a sliver of his interests – and hardly nods to his adventures. A trained nurse, he lives in south London and works for Voluntary Services Overseas. He has a post-graduate degree in wilderness and expedition medicine. And he has travelled around Africa, living in Malawi for two years. “I left home at 18 and went to Côte d’Ivoire. I’ve been evacuated from two wars, once by the British special forces, once by the Americans. I went to Ethiopia when it was in a state of emergency and 10,000 people were arrested. I was in Nigeria during massive demonstrations and we were in lockdown for three days. I’ve had malaria nine times. I’ve been quarantined in a shack in New Guinea for a week because I got a violent strain of measles. I’ve lived in a lot of countries and I really like that adventurous lifestyle.”

No wonder he didn’t flap under pressure in the tent. What about the comments that he looked arrogant? “I was never smug. You’re so nervous that whatever your face is, it’s probably just you trying to be composed. I didn’t know I pouted, but I do. Get over it.”

One of five children, Atherton was brought up by strict evangelical parents in Whitby, North Yorkshire. “We weren’t allowed to watch TV. There was a period where we were allowed to watch one programme a day and you had to circle it in the Radio Times. We had breakfast every morning as a family of seven and my dad did a bible study and everyone had to pray at the end. Some of the things were so nice. We’d play board games and do crafts and cooking together. It was a very loving family and we spent a lot of time together.”

His mother was health-conscious and cooked from scratch. As a result, Atherton grew up vegetarian, without a potato waffle in sight. “In our lunchbox we never had crisps or chocolate biscuits, it would be nuts and seeds. Figs and prunes would be our sweet things. Carrot sticks. We never had butter or margarine. We never had icing on our cakes.

“For my mum, making bread was a way of keeping us busy. She would make the dough and we would play with it like Play-Doh. She would make rolls and we would make rabbits, cats and crocodiles.”

With Steph Blackwell in the GBBO final. Photograph: Mark Bourdillon/Channel 4

His grandmother taught him to sew, knit and crochet. In the living room of the small flat he has just moved into with his boyfriend, Nik, he proudly shows me the practical but stylish things he has crafted: a quilt, bowls and platters (“my Ottolenghi salad plates”), a table and bench (“Honestly, it took about 20 minutes”).

He met Nik, a brand manager who helps him with social media, on a dating site. They are both into fitness. “Our second date was a 100km London to Brighton bike ride. When he agreed to that, I was: ‘Brilliant, this is it.’ We did it not realising it was the big charity one, which was great because all the roads were closed.”

Atherton came out seven years ago by writing to his parents. He chose this method, he says, to give them time to process the news. “The reaction that someone might have from it being sprung on them might not be the reaction they’d want to have if they’d considered it. You’ve been thinking about it for ages, but it’s new for them. I told my parents in a letter and said: ‘Speak to my twin brother before you speak to me because he wants to be able to answer certain questions first that might seem offensive to me.’ They took it very well.”

He loves the fact that LGBT teenagers now contact him for advice, but is aware of the irony. “They say I’m an inspiration, but I didn’t come out until I was 29. But they’re seeing me after that, where I don’t live with shame any more. I’m really happy. Shame just eats away at you. I encourage people that the soonest time it’s right for them, they should come out, because I didn’t do that and so many people you speak to wish they’d done it earlier.”

He says he was frustrated at being “a little bit objectified” early on in Bake Off – “in certain episodes, I felt like I was just a sexual innuendo” – but admits he loves the attention he has been getting since it aired. “In general, I enjoy the buns innuendos. A lot of it is really funny. I mean, I did wear tight trousers every week. It’s not like I wasn’t also playing up to this.”

He would have liked to wear tight shorts and a vest, but it wasn’t allowed. “Apparently armpit hair doesn’t look nice on TV. I think it’s more health and safety, because I said I’d shave my armpits.”

His admirers have certainly been upfront. There are lots of fans in the US, where the show has also aired. “The gay Brits are definitely more dirty. The Americans are: ‘You’re awesome.’ The Brits are: ‘I want to fill you with my buttercream.’ I’ve not just had dick pics, I’ve had videos of people masturbating.”

Aside from the Bake Off innuendo, there were real friendships on show. Atherton, Henry Bird and Michael Chakraverty formed a “least laddy lads’ club” (with Fevronia an honorary member) that lives on through Instagram. “We would ring each other during the week as things went wrong. I’m not embarrassed to say that Henry practised one of my bakes for me – the Aperol domed tart. It was my recipe, but I didn’t have time. He’d gone out the week before and had time to do everything. He sent exhaustive notes. Every two or three minutes were accounted for.”

Atherton thinks this “camaraderie between the bakers” brought a warmth to the show. “You could see that we were helping each other and people weren’t really very competitive. I think that helped, especially in the climate of division and Brexit. I think the public have really liked that.”