The show's frank content has caused outrage. But it's all for our own good, the presenter of C4's Sex Education tells Esther Walker

Anna Richardson wants us all to talk a bit more about sex. And she's leading the charge. "I've been with my other half for about 13 years now," she says, "and when we first met we were shagging all the time. Spin forward 13 years and I get quite excited by fleecy pyjamas, lying in my lovely girly bedroom with a cup of cocoa."

This isn't her talking to me over a cup of coffee, lulled into a false sense of security by the intimacy of a one-on-one interview. She is saying this for a Channel 4, prime-time TV programme, The Sex Education Show.

And she doesn't stop there.

"Maybe part of the reason that my sex life isn't exactly sizzling is because, after so long together, you do let things slide a little bit, physically," she muses. "I've completely let my leg hair go, I've even got toe hair and I've got to confess, as I've got older, I've grown a bum beard."

On the show, she also sits in front of her fridge and uses plastic fridge magnets to number all the people she has slept with (22), tells us there are "period stains" on her pants, persuades a man to have an STI test on camera, and herself goes through a full STI screening, smear test and Hollywood wax (everything off), on camera. And that's just in the first two episodes.

The programme is, at times, really quite stomach-churning in its frankness, but it somehow works, mostly thanks to Anna Richardson's hearty, Staffordshire-lass attitude. "Lots of people have said that I'm brave and honest," she tells me. "I will always say what I mean. Sometimes it's to my own detriment, but it's the thing I value most about myself – that I'm straight and I'm honest. I'm just not embarrassed by anything."

Richardson has been working in television for 15 years, though she might seem like a relative newcomer to our screens. After training as a journalist, she worked behind the camera; one day she was talent-spotted and spent the next six years doing some presenting work on slots at The Big Breakfast. The work dried up, though, and Richardson went back behind the camera, co-creating You Are What You Eat. More recently, she had a guest-presenting slot on the series Supersize vs Superskinny.

"I don't think that The Sex Education Show is like shows that have gone before it, which have mainly tried to show you how to be better in bed," she says. "It's totally different. It's a magazine format, with lots of different parts to it and there's a lot of journalism in there."

Richardson has none of the sly coyness to which presenters of other sex programmes might fall foul. She is tough, no-nonsense and, strangely for a woman with no children, rather maternal. (She had her fertility tested for the show, and discovered that it was very low, which she describes as a "terrible shock".) Despite all this, is she worried that she'll acquire the tag of "That Sex Woman"? She laughs. "Not at all. I admit that as a nation we're incredibly judgmental, and when someone sees the title they might think it's just 'another one of those shows'. But it really isn't like that, so no, I'm not worried."

The UK could do with a bit of sex education. The series interviewed thousands of British teenagers about their attitudes to sex, and the results were scary: 20 British schoolgirls get pregnant every day, and one in 10 teenage girls has chlamydia.

The vagueness of teenagers about sex, says Richardson, was one of the most surprising and worrying things she discovered while doing the show. "What was shocking about the teenagers we talked to is how much stuff they're doing, without really knowing what any of it means or how to deal with it all. They are doing stuff and seeing things that I would never have done at my age. There was no internet when I was younger and we got our sex education from giggling with our friends or from Jilly Cooper.

"Teenagers now have got all this access, and they look at some weird, deviant stuff. And the really terrifying thing is that they are affected by it – they're starting to think it's normal. We looked at some of the porn sites they go to and I was shocked, and I'm not shocked easily. They see ludicrous bodies and think that they should look like that; they think that their penises should be way bigger than is normal; and they see the sort of sex that you get in porn and think that's the kind of sex that other people want."

For the show, a group of teenage boys were shown a series of photos of breasts and asked which pair they liked the most. All the boys chose the surgically enhanced pair. "That was surprisingly anxiety-making," Richardson says. "If all those boys went straight for the surgically enhanced breasts, where does that leave the rest of us? It's worrying, it really is."

Part of the problem, in her opinion, is that sex education in school is underemphasised. What there is "is very biological," she says. "The students actually don't really want their teachers to tell them about it and the teachers find it embarrassing and difficult to be talking about sex one minute and French verbs the next. It's not for me to make a political statement, but my personal observation is that it's a government, parental and personal responsibility to improve things."

The high rate of STIs may well be the consequence of the lack of information available to teenagers. And, perhaps, of the stigma surrounding such illnesses. Many people might have been embarrassed by an early sexual-health conversation with a doctor or nurse and been put off going back.

"I can completely sympathise with people who feel like that," Richardson says. "I had an experience when I was at university with a pregnancy scare and they were pretty snotty about it in the clinic. They had the attitude of, 'Oh well, you've got yourself into this position, how are you going to get yourself out? More fool you, you silly girl.' I can see why a lot of sexual health stuff is driven underground. People don't want to be judged and stigmatised, so they don't go to get tested.

"But, really, it is incredibly easy to get it done. You can walk into any family planning clinic, any sexual health clinic, or you can pay to go privately and get tested that afternoon – and there are some results that you can get instantly. So the answer to why people don't get tested enough is that people are either too afraid to go, or they can't be arsed. I just don't think there's enough of a threat, it doesn't seem real enough – particularly chlamydia, which is mostly symptomless.

"When I had an STI screening for the show, yes of course it crossed my mind that I might have something, because I hadn't been tested for years. It was a genuine fear. But the thing about STIs is that they're all treatable. It's a little bit like having a cold, or measles. The only difference is that there's a huge and unhealthy stigma about it – just because there is that extra burden of personal responsibility when it comes to STIs. But, really, it is much less of a big deal than people make of it."

The programme is also a personal journey for Richardson. She discusses how the spark of lust has dimmed in her 13-year relationship, and investigates how she can reclaim it. What did her other half think of that? "My boyfriend is in the TV industry, too, so he understood what I wanted to do with the programme. He was very supportive about the whole thing but he said that he didn't want to be included in the series. ...He's very open-minded but yes, I think he feels a little bit peeved and affronted, as a man, that I suggest that after 13 years our sex life isn't red-hot and sexy every single night."

Teens and sex: The facts

30% of 14- to 17-year-olds said they have had sexual experiences under the age of consent

More than a quarter of the boys, 27%, said they access porn every week

Over a third, 34%, said that sex is not discussed openly in their family

29% of teens said they do not understand the medical processes involved in having an abortion

16% of 14- to 17-year-olds did not know that there is no cure for HIV/AIDS

40% of 11- to 18-year-olds thought their sex/ relationships education was poor or very poor

73% of teens felt that sex/relationships education should be delivered under the age of 13

55% of all 12- to 15-year-olds had not been taught how to use a condom