By the time David Davies and I part company, he is looking anxious. "The easiest thing for me to do would have been not to do this interview with you, that's the truth," he worries.

"I haven't done years of diversity training, so sometimes I say things which are probably tactless, and I don't mean to, to be honest, I don't mean to do that. But these feelings are hard to articulate, and the trouble is that if you try to, and get it wrong, which I probably, frankly, am doing now, you're going to get no end of abuse for it, and upset a whole load of people, some of whom I actually quite like. This law is going to happen, and the best thing to do is just shut up and accept it, really, which is probably why I shouldn't have accepted this interview. Too late now."

It's two weeks since the Tory MP told Radio Wales that gay marriage was "barking mad", and that "most parents would prefer their children not to be gay". He seems a bit shell-shocked by the subsequent uproar, so his decision to give his only follow-up interview to us, "the enemy", is impressively brave. At times there is a hint of hung-for-a-sheep recklessness about him, at others a bewildered but cheery hilarity ("My favourite tweet was: 'If you were gay you'd have a nice suit that fitted and wear product in your hair.' Do you think I should retweet it?"), and most of the time it's as if he's not giving an interview so much as thinking aloud. There's no spin, let alone a line, and the sincerity of his soul-searching is really charming, even if he is all over the place. Davies's confusion about homosexuality isn't all that unusual, and you will have come across it before – just probably not in anyone running the country. He is without a doubt the most guileless and gauche politician I have ever met.

His big worry about gay marriage, he explains, is that it will necessitate a revision of sex education. "This is where it gets sensitive, but I've got three kids, and I know a lot of people with children have got this concern. I hate to say this, I hate to say this, and I don't want it to cause outrage or offence … " He looks down and shifts awkwardly. "But I suppose, at a certain level, I see heterosexual sex as being – and it's probably the wrong word to use – but the norm. I think it's reasonable to say that the vast majority of people are not gay." He hesitates, sighing. "I just worry if children are going to be taught that [heterosexuality] isn't necessarily the norm, and that you can carry on doing all sorts of other things, are we going to have a situation where the teacher's saying, 'Right, this is straight sex, this is gay sex, feel free to choose, it's perfectly normal to want to do both. And you know, why not try both out?' I mean, are we going to have that?

"Can I say something else as well?" he adds. "It may or may not be relevant." When Davies was 16, a popular school friend had announced he was gay. Davies ran into him again at 19, "And it turned out the guy had got engaged. To a woman! And he absolutely didn't want to talk about what had gone on between the age of 16 and 19. He'd started coming down to the pub at 16 with, you know, splits in his jeans, and started buying Erasure albums, and all the rest of it – and three years later he's suddenly horrified by the whole thing!

"I suppose what I'm trying to say, in a very clumsy way, which will again probably cause offence, is that some people might be going through a bit of a funny phase between the age of 15 and 20 when they're not sure. And I'm not absolutely convinced it's a good idea to be changing sex education in school to try and say to people, 'Feel free to go out and experiment and do this, that and the other.'"

Had Davies's teacher told him that when he was 10, would he have been tempted to try being gay? He practically jumps out of his seat, exploding in incredulous giggles. "I reckon in my case, almost certainly not." So what exactly is his worry? "You see, it's not so much telling them it happens. It's explaining in a certain amount of detail how it happens." I must confess to having never obsessed about the details of sex education. What does he mean? "If you're going to explain the facts of life you've got to explain at some point, penis, vagina, they go together, this is how children are made. Well, do you also have to start explaining in similar detail how gay sex is carried out?" I'm far from sure you do, actually, but more to the point, no amount of familiarity with homosexual mechanics would have turned my 10-year-old self into a lesbian.

"But you're a lady, you're a woman, so you wouldn't have felt quite the same way. I mean, at school the girls all went out and bought Erasure without any issue." He's being perfectly serious. But what about the lesbians in my class – what would have helped them? "Oh, I don't know what they went out and bought." No, I mean what about them feeling confused and excluded? "I wish there was some way round this that meant they didn't feel excluded, I really do."

Let's say he's absolutely right. Gay marriage will mean more gay sex education, which will make more of us gay. Can he explain what would be so bad about that?

"No, I don't think I can, to be honest. I don't think I can explain it. I can see immediately, if I did, that it would cause offence to some people – and that's wrong, isn't it? But I'm not even sure that I can answer your question very well, anyway. I can only say I have a slight sense of unease."

One thing he does want to make very clear is that when he said most parents would rather their children were not gay, he did not mean they would reject a gay child. "If one of my children were gay I don't think it would make any difference to the way I felt about them at all. I would want them to be happy and contented." Surely, then, he would want a society which made that possible? "I think you're probably right." Suddenly he looks a bit lost. "And it's something I've got to search for myself. It's just very difficult for me to answer your questions."

When I ask why he hopes none of his children will be gay, he admits again, "I don't know why. I find it hard to explain, frankly. But I'm uncomfortable with it. I suppose it's a grandchildren issue, perhaps?" he offers doubtfully. "Isn't it a natural instinct? Maybe that's the problem – it's hard to rationalise an instinct with politics in a logical way, which you're trying to do. But I've got this sense of unease. I think it's widely shared – I know it's widely shared; you should see the emails I get. I think a lot of people have this slight sense of unease, which isn't very well articulated. And I'm afraid I haven't articulated it very well."

Sometimes, I tell him, when I find an argument really hard to articulate, that's because it's wrong. "You may be right. I may very well be wrong about this. But I'm not sure I'm wrong. It may just be that I'm a victim of the era I was brought up in."

Born in 1970, Davies grew up in Newport, joining the Territorial Army in his teens. After comprehensive school he went travelling in Australia, before returning to work as a lorry driver for his family's haulage company. Having campaigned against devolution in Wales, in 1999 he was elected to the Welsh Assembly on a platform of opposition to any further devolution, and won Monmouth for the Conservatives in 2005. He is a special constable, and an amateur boxer.

"I make no bones about it, I'm a product of my upbringing and of the time I was brought up, so I'm not going to pretend not to be. It's not like I was brought up in San Francisco or somewhere like that.

"But I'm changing. This is going to sound quite appalling, but nobody in my circle of friends in 1986 would have admitted liking Erasure, or would have been seen dead going out and buying a Boy George CD. Now I've got Boy George's greatest hits, and I love it!"

When civil partnerships were first introduced, "I probably wouldn't have been a huge fan, let me be honest," but now he's changed his mind. Section 28? "Mmm, I probably would have worried about repealing that." Reducing the homosexual age of consent? "I'd have probably been against it, in truth." But he wouldn't dream of reversing these policies now, "So yes, I take your point, I am changing." Given time, could gay marriage be another one? "It might well be, it might well be, and I'm perfectly happy to accept that you may be right."

All of a sudden, he seems to panic. "So far all we've talked about is gay marriage. And I want to tell you I'm not obsessed with the issue. I don't spend every waking moment of the day speaking about gay marriage, at all."

That is unquestionably true. In fact, I'd guess he's given less thought to it than not just most MPs but most people in the country. After all, there can't be many left who would share Davies's mystification at something a closeted gay colleague said to him years ago.

"We were at party conference and he was saying to me – and this is a direct quote – 'Look at all these poofters! Bloody poofters, eh?' He was quite senior in the party, and I knew he was gay, but I don't think he knew I knew. And I thought, why are you saying this? Why are you pretending to mind all about all these 'poofters'? Why?"

In a way it's quite comical that Davies should end up at the forefront of a debate about something he cheerfully admits to not really understanding at all. He's much more concerned about "issues affecting lower-middle-class, working-class people", and lists deficit reduction ("if anything I might go faster"), law and order ("I do think prison can work"), immigration, multiculturalism and Europe ("I'd want a referendum, and I'd probably vote out"). It sounds a lot like what Ukip stands for.

"Well, maybe what Ukip's saying represents what a lot of Conservatives stand for – that's a different way of looking at it." He says he would never defect, but his own mother – a working-class miner's daughter, and lifelong party activist – already has. "And it's a real worry. The Tory party's core supporters are peeling off to support Ukip."

Davies wishes our mainstream parties could debate what the Americans call culture wars, "without everyone jumping up and down in a rage". Why, only the other day he was having a conversation with someone at the Equalities and Human Rights Commission, and wished it could have been in private. "Because he was telling me what it was like to be a young black man searched by a police officer. And I could have told him," he exclaims delightedly, "what it's like to be a police officer, trying to search someone who didn't want to be searched!"

For a moment I think he's joking, but Davies really does see these two experiences as analogous. Registering my amazement, his face falls.

"What? Oh no. Have I said something wrong again? Have I said something really bad? What did I say?"