“The most successful British musician most people have never heard of,” declare the posters for Steven Wilson’s new album. They may be right. Wilson can fill grand venues, while 2015’s Hand. Cannot. Erase, reached No 13 in the charts, and his new album reached No 1 in this week’s midweek charts. But he is never on the radio or TV and seems as likely to get invited to play at Glastonbury as receive the proverbial audience with the Pope.

“I’m invisible in the mainstream,” he sighs, sipping tea in his Hemel Hempstead summerhouse. “I can roll into town and do two nights at the Royal Albert Hall, and nobody notices except my fans.”

The 49-year-old has been dubbed “the king of progressive rock”, which has helped build a huge cult following, but has also ghettoised him in pop’s last toxic, unrehabilitated genre, associated in the wider consciousness with po-faced ageing males, interminable noodling guitar solos and daft symphonies about space. Which isn’t Wilson’s idea of prog at all.

“Every time the mainstream media talk about progressive rock, they wheel out a clip of Rick Wakeman in a cape,” he says. “For me, it’s one of the most ambitious forms of music. The problem is that when it doesn’t work, you end up with Emerson, Lake and Palmer doing symphonies with 60-piece orchestras and revolving pianos, which I think is ridiculous as well.”

Wilson finds the “king of prog” mantle “flattering, but uncomfortable”. He has made an astonishing 50 albums, more than half of which aren’t remotely prog. He has done ambient noise (as Bass Communion), postmodern psychedelic rock (as Porcupine Tree) and dreamy trip-hop (as No-Man). His new solo album, To the Bone, features squalls of furious guitars and occasional shifting time signatures but is mostly artful, sophisticated pop-rock, channelling the favourites of his youth: Talk Talk’s The Colour of Spring, Peter Gabriel’s So, and Tears For Fears’ Sowing The Seeds of Love. The single, Permanating, is unashamedly euphoric pop – inspired by ELO and Abba – which, ironically, has upset some fans for not being prog enough. One Spanish fan-journalist even booked an interview and flew to the UK to tell Wilson that his new music was “shit”.

“But I love that,” he says. “Pop shouldn’t be a comfortable slipper. It should shock and surprise you, and confront your expectations.”

This is one of Wilson’s key beliefs, and perhaps why, in formulaic times, people are turning to his music for something more sweeping, emotional and catholic. In person, he isn’t po-faced, but self-deprecating and infectiously enthusiastic. He says no genre should be out of bounds, and in taking fewer risks, most contemporary pop has become “boring … What’s lacking is that will to risk landing on your face. I’ve never understood this concept of ‘guilty pleasures’. Why be guilty? It’s all great pop.”

While Wilson was growing up, his dad listened to Pink Floyd and Mike Oldfield, and his mum loved Abba and Donna Summer. “The whole thing was magical. It wasn’t until secondary school that I realised that there were snobberies and borders around music, but by then it was too late.” His teenage mixtape consisted of “[80s 4AD post-punk band] the Wolfgang Press, Cocteau Twins, A Certain Ratio and Pink Floyd.”

Steven Wilson performing at the City Hall, Newcastle in February 2016. Photograph: Camila Jurado

He formed his first band – psychedelic duo Altamont – when he was 15. Porcupine Tree’s 1993 opus Up The Downstair channelled “the Orb and the Future Sound of London, but also Floyd and Ozric Tentacles. If I liked it, I didn’t give a fuck.” At the height of grunge and Britpop, Wilson listened to A Tribe Called Quest, Japan and the Rubettes.

To pay the bills, he made commercials (including one for the Observer). “The irony is that a lot of these journalists who’ve never heard of me were hearing my music all the time,” he says. “It was all over TV in the 90s. That gave me freedom to keep doing this music that wasn’t reaching an audience.” But then gradually it did. Despite a “war of attrition” to get media coverage, playing to “four people in a pub in Carlisle” became “the Borderline, the Scala, the Forum, then suddenly the Albert Hall”.

His breakthrough fourth solo album, Hand. Cannot. Erase, was inspired by the death of Joyce Carol Vincent, who lay undiscovered in her flat for three years, but he admits it is really “about me, being invisible in plain sight – a metaphor for my career”. To the Bone, meanwhile, articulates contemporary powerlessness: “social media disconnection, refugees, religious fundamentalism … It’s very much grounded in the world I live in, another thing that sets me apart from progressive rock.”

But lately, Wilson has found himself at the forefront of a groundswell of associated acts – including reinvented Swedish former death metal band Opeth, whose last album breached the UK Top 20 – who also have the potential for even broader appeal. We are still speaking when a text informs Wilson that BBC Radio 2 is playing Permanating. Would the UK’s biggest underground artist like a hit?

“Even though I’m pushing 50 and wear glasses, there’s still a little part of me that would like to be Prince or Marc Bolan,” he grins. “But mostly I’d just like something to act as a doorway to my back catalogue. Everyone has decided whether they like Muse or Radiohead. Most people have never had the chance to make that choice with my music because they don’t know I exist.”

• To the Bone is released on 18 August on Caroline International. Steven Wilson will tour in 2018.