NOT that you particularly need to know this, but there are only two pop stars whose haircuts I ever tried to copy. Some time back in 1983 I gave my sister the sleeve of Orange Juice’s Rip It Up album, and said, “I want that,” pointing to Edwyn Collins’ mixture of shaved sides and floppy fringe.

Then, seven or eight years later, I went into Torpedo in Stirling and asked for a Neil Tennant. (Torpedo is still trading but I don’t think my hairdresser Nadine works there anymore, so don’t go thinking you can do the same.)

This would have been around about the release of Behaviour (the best Pet Shop Boys album), so I’m guessing the visual reference would probably have been the video for the single So Hard.

Memories. Would that either of us – that’s me or Neil just to be clear, not Nadine; she had her own thing going and didn’t need to take style lessons from thirtysomething (now sixtysomething) pop stars or their fans – looked like that now.

Still, even if Neil Tennant may no longer have the hair he had back then, everything else about him that you would want to imitate remains present and correct. He remains the thinking pop fan’s pop star; erudite, funny, knowing, a man fascinated with the world around him, engaged with politics and culture and, most importantly, even at the age of 65 still with an unashamed love of pop music.

Age, then, has not wearied him. “My father, when he was my age, had been retired for two years,” he points out. “I’m going on tour. We’ve got a new album coming out.”

If anything, Tennant, the one-time Smash Hits journalist, and his partner in pop, former architecture student Chris Lowe, are as busy as ever. Last year they wrote the music for a theatrical version of My Beautiful Laundrette, and worked on Musik with playwright Jonathan Harvey, a one-woman show for actor Frances Barber which is now about to transfer to the Leicester Square Theatre in London after a run at the Edinburgh Fringe. (“That was fun,” Tennant says. “It rained every single day. Every. Single. Day. Frances was in the Spiegeltent and it was pouring and there was a drunk singing outside. It was like playing the old working men’s clubs.”)

And then there’s the aforementioned new album and the tour. In short, retirement is not an option.

“When do men get a pension now? Does anyone know the answer to that question? We were discussing that at lunch yesterday. Is it 67? I said 68.”

It’s actually still 65, changing to 66 later this year, but anyway, Tennant is not planning to draw his own pension any time soon.

It is December when we talk. Tennant is just about to disappear to meet Lowe so they can go and buy their manager a Christmas present (maybe a handbag, he thinks). Until then he is chatting to me about Christopher Isherwood, Berlin, being an “electronic purist”, heterophobia and internationalism.

There is the odd thing that he politely refuses to talk about. “Oh, that’s a personal question,” he says when I ask him to tell me the last time, he broke someone’s heart. “How do I know that I know the answer?” (He is slightly more forthcoming when I ask the last time he had his own heart broken. “Ten years ago, maybe.”)

And as for the state of his heart nowadays? “I prefer to be Neil Tennant, man of mystery,” he says.

Never mind. There is so much else to talk about. Maybe we should start with the new album, though. To do that we need to travel to Berlin.

For the last decade the Pet Shop Boys have owned a flat in the German capital. “It’s got a very different energy from London,” Tennant says. “It’s just a much more relaxed city than London. We just find it very productive and enjoyable.

“We’re away from all the pleasures of London. In London, we stop working at six o’clock. We work later in Berlin.”

That commitment has now resulted in three albums that have proved a splendid late flourish in the Pet Shop Boys discography. The latest, Hotspot, is as fresh as anything they’ve ever recorded. Not bad for two men in their seventh decade on the planet.

“With this we’ve now made three albums with [producer] Stuart Price. Our idea for them was that we were going to be electronic purists. So, no orchestras or acoustic instruments. We’ve actually broken that on this album with one track, Burning the Heather, with Bernard Butler playing acoustic guitar. Otherwise, on the trilogy we’ve been electronic purists for the first time in our career.”

As ever with the Tennant and Lowe, the result offers crisp beats allied to romantic melancholy. Like the best pop music, it is happy-sad. And as ever, there’s a range of references that go beyond most pop songs.

For example? Here is Tennant talking about the opening track, Will O the Wisp: “I got the idea from reading about Christopher Isherwood returning to Berlin after the war and meeting up with one of his old boyfriends who at this point was married.” That’s very Pet Shop Boys, isn’t it? Pop music making no distinction between low and high. Pop art if you like. (They once did a compilation double album that was entitled precisely that, remember?)

Anyway, Tennant married that vision of the author of Goodbye to Berlin to the idea of the U1 train on the U Bahn, which travels west to east in Berlin and, come Thursday night, is very much a party train.

“We sat on the train with Stuart Price and recorded the entire journey,” Tennant says. “Apart from when part of the journey was replaced by a bus service. Don’t think it only happens in Britain. And I really like the fact that on the track you can hear the train and the whole atmosphere.”

A sense of movement has always been appealing to Tennant. The very first track on the Pet Shop Boys’ first album, Two Divided by Zero opens with the lyric, “Let’s not go home, we’ll catch the late train,” he reminds me. “There’s always been this theme of running away.”

It’s a reflection of the band’s internationalism. It’s a trait that right now seems out of step with the rest of the world.

“Oh yeah, absolutely. It’s classic that in the middle of Brexit the Pet Shop Boys have made an album in Berlin. We’ve always seen ourselves as European.

“We’ve always been very lucky to have a career that takes us all over the place. On YouTube they can tell you in which cities you get most views and the Pet Shop Boys number one is Mexico City and number three’s Rio, I think. Or Sao Paolo. London comes in sixth or something. That’s something that we feel proud of.

“In Germany Pet Shop Boys are as known in Germany as we are in the UK. We’ve got a list a mile long of German newspapers to speak to next month and that’s great, I think. It’s an amazing thing that people are still interested.”

Well, yes, but at this point it’s probably worth remembering how big the Pet Shop Boys were at their peak in the late eighties (their “imperial phase” as Tennant has always called it). They have sold somewhere in the region of 70 million records (and that’s one of the more conservative estimates). For a while there back in the second half of the 1980s the Pet Shop Boys were pop.

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In the years since they have diversified into providing music for ballets and films and theatre (see above). But they have never stopped making pop music. They’ve had peaks and troughs in the 1990s and the 21st century but they remain in the game.

“There’s a time when you can do no wrong,” Tennant suggests, “but, then, even if you do good work, people get cynical. They always want to think you’re just quote ‘doing it for the money.’ And you’re not, really.

“And then people decide they always liked you. I’m not saying we’ve totally reached that, but it’s a little more like that nowadays.

“Everyone likes Abba now. People used to hate Abba, people thought Abba were the naffest thing in the world. But no one can deny the quality of those songs even if maybe sometimes we’ve heard them too many times.

“And I think with the Pet Shop Boys you have to admire the quality of the song writing, the way it’s been maintained over the years. To blow our trumpet a little bit. I don’t think many people have done that.”

Does he still listen to new pop? “I do. I don’t think it influences us melodically. We sometimes worry that we write long and languid melodies, whereas nowadays everything is like a nursery rhyme to me because … it sort of is.”

Of course, the career of the Pet Shop Boys meshes with huge changes in pop culture and the wider culture it reflected. When they made an impact in the mid-eighties with West End Girl, pop was still, with a couple of notable exceptions (Jimmy Somerville and Holly Johnson), wary of openness about sexuality. Everyone from Freddie Mercury to George Michael veiled their sexuality until circumstances (Aids and arrest) forced their hand.

Tennant himself came out in Attitude magazine in 1994. “Oh God, 25 years ago,” he says when I bring it up. “John Major was Prime Minister.”

His experience of growing up gay in the UK in the 1970s and 1980s must be so different to that of, say, Olly Alexander, front man with Years & Years, who guests on the Pet Shop Boys track Dreamland on the album. Alexander was born in 1990.

“I am old enough to be his father,” Tennant admits. “I’m practically old enough to be his grandfather … No that’s an exaggeration. Yes, his generation is so different.

“Mind, that’s not a gay thing. I realised we grew up in a more rough-and-tumble kind of way. Teachers used to throw blackboard dusters across the room and things like that. I wrote a lyric years ago. This Must Be the Place I Waited Years to Leave. Well, I mean they couldn’t do that nowadays. I think we just grew up in a more violent time.”

He thinks about this a moment and remembers the current spate of knife crime in the capital. Still, he says, London back at the start of the 1980s could be frightening.

“Chris and I used to go to some bar in Angel Islington. You were always scared on the way back that you were going to get beaten up by a skinhead. And I grew up in Newcastle in the seventies. Terrifying.

“I dread to think what Glasgow was like in the seventies. Newcastle was pretty bad. So, you grew up in a very different culture which made you a very different person.”

Still, Britain’s attitude to sexuality has changed remarkably in those 25 years. These days gay marriage is a thing. “And anyone can get a civil partnership now,” Tennant adds. “It was Peter Tatchell who pointed out that civil partnerships were heterophobic. And I know heterosexual couples who don’t want to get married. I don’t know why you don’t have a civil partnership in case something happens to one of you. The other one has no rights whatsoever. It would be a real nightmare to everyone concerned. You don’t have to go through the whole white wedding thing.”

Does he approve of gay marriage? “I think equality is right. It has to be there otherwise … people aren’t equal. I think we’ve moved on from people being tolerant of gays, which sort of implies prejudice doesn’t it? ‘I don’t like this, but I’m prepared to put up with it.’

“I always thought - I used to say this in the eighties and the nineties when I was accused of being closeted - you shouldn’t judge people on their sexuality. I actually think it’s sort of restrictive because it puts people in little ‘straight’, ‘gay’ and ‘in-between’ boxes and I don’t necessarily think life is quite as straightforward as that.”

“When it happened, the old gay part of me thought, ‘God, all these gays are like straight people, getting married and going to the PTA meetings with their kids.’ But you know what, I think it’s a good thing.”

It’s almost time to go. He has a Christmas present to look for. Before he does, I say, I want to do a quick thought experiment. I want him to imagine a parallel universe where Neil Tennant didn’t become a pop star. What would he have been? A teacher? “Never. Would never have done that. Never had any interest in doing it. It looks unbelievably pressurised. Even now I occasionally get asked to do something at a university and I say I will answer questions, but I won’t give a lecture because I don’t have anything to say.”

Neil Tennant the priest? “Well, I did want to study for the priesthood when I was 10 years old.”

That’s like every Catholic boy, isn’t it?

“Oh, I don’t think so. I wanted to go to the seminary. Now closed down. My parents said, ‘Why don’t you wait until you’ve done your O Levels and then you can think about it again.’ Well, of course, it never happened. That desire was gone by the age of 12, probably earlier.”

Finally, Neil Tennant the one-hit wonder? If their debut West End Girls had been their only hit, would he be doing the Rewind Festival thing, turning up between Spandau Ballet (sans Tony Hadley these days, obviously) and Clare Grogan?

“Neither Spandau Ballet nor Clare Grogan were one-hit wonders,” he points out, ever the pop scholar. But, no, he says, “I don’t think I would have done that.”

Actually, he reminds me, there was a time when it felt like Pet Shop Boys were one-hit wonders. “West End Girls was number one all round the world and then [second single] Love Comes Quickly got to number 18 or 19 something like that, so we had to fight our way back.

“I don’t know what would have happened. Never mind what would Neil Tennant have done what would Chris Lowe have done? Become an architect? Maybe he would have done, I don’t know.

“I had written songs all my life so I would probably have carried on doing that.

“I would probably have started doing some freelance journalism. Mark Ellen might have offered me a job on Q.”

He would have been good at it too. But he’s a better pop star. Long may he shine.

Hotspot by Pet Shop Boys is out now. Musik opens in the Leicester Square Theatre, London, on February 5. Pet Shop Boys play The SSE Hydro, Glasgow on June 6

NEIL TENNANT’S CELTIC CONNECTION

Your family has Scottish roots, Neil. Can we claim you?

“My brother and my cousin have been doing our family tree. We can get back to the 17th century in Stirling. Actually, I applied to Stirling University but I didn’t get a place.

What were you going to study?

History and archaeology. Why I was drawn to archaelogy is one of the things that puzzles me. I’ve still got no interest.

The family moved to Edinburgh and then, in the 1870s, Berwick. Then they moved to Newcastle.

“My mother’s family was Irish. It often amuses me because I’m often described as typically English but I’m actually a Celt and I’m just doing a good imitation.”