LET’S start with a musical history lesson. When he was a teenager Nitin Sawhney played in every kind of band imaginable. He would turn up in jazz quartets and youth orchestras and punk bands. At one point, he says, he was even in a Van Halen covers band. And an AC/DC covers band. “Playing lead guitar,” he says.

The strangest one was maybe the heavy rock band called Dark Angel he was part of when he was in his early teens.

“The lead singer was only 14, but he already believed he was a superstar,” Sawhney recalls. “He had the messiah complex going on. He would turn up for band rehearsals and say, ‘We need to talk about how we get coaches for all the fans for the gig we’re doing next week.’

“I’ve come across a lot of people who had no career but who really had that mentality. And you think, ‘How have you arrived at this conclusion?’”

Nitin Sawhney is quick to tell me he’s not the Messiah. But he is a very creative boy. He’s a musician and producer who can turn his hand to anything, from dance music to film and TV scores (including Mowgli and the TV series Human Planet). He was there at the birth of the Asian Underground scene at the start of the 1990s. He’s conducted the LSO, had one of his albums, Dystopian Dreams, was turned into a stage show at Sadler Wells. He has earned a Mercury nomination and a MOBO award, a Bafta nomination and an Ivor Novello award too. He turned down an OBE some years back but recently accepted a CBE (for his late dad). He even was in a comedy duo with Sanjeev Bhaskar and was in at the start of the sketch show Goodness Gracious Me. Not too shabby a CV, all told.

And that’s before we talk about his collaborations. He was worked with everyone from Sinead O’Connor to Paul McCartney, who, he says, could have been a “right a***hole” if he wanted because, well, he is Paul McCartney. But he wasn’t. “He was the easiest person I’ve ever worked with,” Sawhney says. No Messiah Complex then? “He had no ego. He was really chilled.”

I’m not sure you could say the same about Sawhney, though. Talk to him for any length of time and it’s quickly apparent his good humour and natural curiosity are tempered by anger and frustration. The reason? Take your pick. Brexit. The rise of racism. The demise of multiculturalism. Nigel Farage. Katie Hopkins.

Music and politics inevitably cross over. This morning Sawhney is in his studio in London. When he is in London he’s usually in his studio. “I pretty much treat it as a normal job. I come in from nine to six, but often it can be quite a bit later, depending on what I’m doing.”

After speaking to me he will return to working on remixes for his first single off his new album. It’s called Immigrants. In this case the album will be wearing its politics on its sleeve. Literally.

And when Sawhney visits Glasgow later this month his Celtic Connections show will draw heavily on his album Beyond Skin, which celebrated its 20th anniversary last year.

Two decades seems a long time ago, he says. “And yet the subject matter seems more relevant than ever. I find myself so totally pissed off most of the time about what’s going on right now. Across the world, but particularly in this country, America, even in India. It’s frustrating because it feels like there is no respite from the mad onslaught of bull**** that is going on.

“Beyond Skin was about challenging perceptions of identity, race, nationality and I still feel annoyingly that it is a very relevant album.”

If anything, you might say, 1999 felt a better, more optimistic time than now. “Yeah, 100 per cent. But back then I was still smarting from all the crap that happened in the seventies and eighties.”

Well, quite.

To know how far Nitin Sawhney has come it helps to know where he started. Born in 1964, he was the youngest of three brothers who grew up in Rochester in Kent. His dad worked in the oil industry. His mum had been a classical Indian dancer. He grew up in a house where music was constant. “My mum and dad both listened to Indian classical music, but also flamenco, Cuban music, a lot of crooners and a lot of pop. My brothers listened to a lot of rock music. So, I was listening to everything from the Doors to Led Zeppelin and a lot of jazz.”

That array of influences must have fed into his desire to explore every avenue in his music-making. “A lot of those things found their way into my playing,” he agrees.

He started playing the piano when he was a young boy. Ask him for his first musical memory and he talks about banging the piano keys when he was four years old, thrilled by the sounds that emerged. “That feeling, I don’t think, has ever left me. Whenever I see a piano at a train station or an airport or in a bar, I’ll always feel a massive urge to go up and play it.”

But at the same time as he started to learn piano he was also being introduced to the reality of life as one of the few Asian faces in a predominantly white town.

At school he began to be bullied from the age of five. He was called “curry face” and even physically attacked at times.

This was the era of Enoch Powell’s infamous “rivers of blood” speech and its long and bloody tail. The National Front leafleted at Sawhney’s school gates. Earlier this year he told Lauren Laverne on Desert Island Discs that he was once followed home “by a guy in a van shouting out racist abuse at me”.

Why, you wonder, would van man waste his time? “Because there weren’t any other Asians around,” Sawhney suggests. He had found someone to vent his rage on. It was that simple.

The same mindset is all over social media now, he says. “I block people every day because of the madness that I still get. Twitter doesn’t do anything about it, by the way.”

Back then did his parents suffer from racist abuse too? “Yeah, I think they did. But they kept it from me, and I kept it from them. We lived our lives wanting to keep a happy tone in the house. It was quite weird. I had this dual identity. When I was in the house, I was always trying to be optimistic. But, ultimately, I hid in my room a lot and played music because I didn’t like the false nature of not talking about what was happening.”

It was only later that he learned what his mum and dad were going through at the same time. “And it was just because we lived in an area that was really, really racist.”

Right now, he says, it feels like that time is coming back. He talks about Katie Hopkins having a go at him for defending Stormzy on social media and accusing him of being racist against white people. The right is hijacking the terminology and turning it against the people who have been historically its victims, he believes.

I want to go back to that young boy, I say. In your Desert Island Discs interview, Nitin, you said that when you grew up you were angry with the boy you had been. “That’s right, yeah.”

I wonder when you realised you should forgive him?

“I’m still in that process in a lot of ways. It was a surprise to me that I felt that way, to be honest. It was something that came out in therapy. But I get why. The reason why is because I was frustrated by the fact that I wasn’t strong enough.”

You were just a boy, I say. “It’s not a logical thing. I just wasn’t strong enough to be able to stop people doing things to me or manipulating me or controlling me or just literally attacking me. I felt that I was powerless, and I hated that feeling.

“When I look back at that person I was, I see a powerless kid. And it frustrates me. I don’t want to be that. I think there’s a loathing that comes from thinking of myself as powerless. I hate that side of me, the side of me that has no power. And I think that’s probably the case with anyone who has come from abuse of any kind.”

When did you feel you did have power? “I think performance was a big thing. Being in bands, doing comedy with Sanjeev, being a DJ. Anything that involved performance. It was about taking control of the crowd. It was never about wanting to show off or anything. I’ve never really had that need.”

Music was his way out of Kent, although Sawhney hedged his bets by first studying law and then accountancy. Then there was a chance of a career in the mid-nineties in comedy with Goodness Gracious Me. But music was the greater pull.

His first album Spirit Dance came out in 1993. By the time Beyond Skin, his fourth, appeared, in 1999, he was very much part of the rising Asian Underground in the UK. “The nineties were fantastic,” he says, with voluble enthusiasm.

“We were getting played a lot on the radio. Getting playlisted on Radio One was an amazing moment. There was a genuine upsurge and it felt like exciting times.”

And then everything changed again after 9/11. “If things had carried on as they were, we would be in a very different world now. It does interest me what would have happened if Al Gore had become president, which he should have rightfully,” he says, conjuring up memories of the 2000 presidential election and those hanging chads in Florida. “What that might have meant on issues of climate change, on issues of race and nationality.”

Instead, the west was engulfed in paranoia and fears of otherness. “I was in America on 9/11 and I was stopped, I think, five times, on the way to a plane. Maybe more. They just said, ‘You fit the profile.’ A lot of people are brown.”

9/11 changed everything, he says. “Until then, I think, multiculturalism was being portrayed in a very positive light. Sadly, we’re living the legacy of 9/11 even now with the rise of people like Farage.”

Sawhney’s next album, due out late spring or early summer, will be called Immigrants

It’s also his own family’s story of course. “They were quite brave,” he says of his parents. “Immigrant families tend to be.”

Crossing borders. It was their story and in a way it’s his too.

“Borders are a construct of people who are lucky in their lives. When we think of borders – or any kind of geographical elitism – it’s been created by people who are very fortunate. If I think of idiots like Katie Hopkins or Nigel Farage, all I think is, ‘Well, you are so privileged to be in the position you are in and it’s just so disgusting how you patronise and treat other people, thinking that you are inherently better than they are.’ That’s what makes me sick.”

But Sawhney’s not without hope. There are good people in this world, he says. Whether it’s Greta Thunberg or his mates. “I think people who care and have a conscience ... that gives me hope. Because those people aren’t willing to sit back and let the world turn to shit.”

Nitin Sawhney is a citizen of the world. He hopes the rest of us will realise we are too.

• Nitin Sawhney plays the Old Fruitmarket in Glasgow on January 28 as part of Celtic Connections

NITIN SAWHNEY’S CELTIC CONNECTIONS

“I love music from Scotland anyway. There are certain nuances that feel quite familiar within music north of the Border; how you bend notes in Celtic music as well as in Indian classical music

“Sometimes if I hear a violinist in this country [England] they are less likely to have that kind of sound that I am looking for than people who have played Celtic music or played Arabic music or Indian classical music so I tend to relate more easily to Celtic sounds.

“Also, the idea of ballads and laments. I love that tradition and there is something very moving and touching about that sound. And the power of Celtic music is very much, I feel, about expressing your soul. And that’s something I will always look for.”