Mike Rosenberg: Passenger with fame on his itinerary

'Let Her Go' was a huge hit for Mike Rosenberg but it hasn't stopped him from busking, as Charlotte Cripps discovers

Branching out: busker-turned-hitmaker Mike Rosenberg (David Sandison)

Passenger (aka Mike Rosenberg) had the biggest selling single in the UK last year, with his song, "Let Her Go". It was a surprise for the then unknown musician that his casually written song about the ending of a long relationship became No 1 in 18 countries worldwide. He then won an Ivor Novello award last month for the song, beating off Emeli Sandé and Olly Murs in the most performed work category. Now his new folk pop album, Whispers, has just entered the top five in the UK charts and, while it may not churn out another mega hit, Rosenberg is definitely here to stay.

I meet Rosenberg in the street and help him drag the giant ice-hockey bag in which he keeps his guitars into the atrium of a building to do the interview. Despite his newfound success – his UK tour in November sees him play venues such as London's Hammersmith Apollo and O2 Dublin Arena – Rosenberg still busks to keep in touch with his fans, and for people who can't afford a ticket.

On his new album Rosenberg, 30, who has a neat beard and polite demeanour, sings about love, death, growing up and getting old. His voice has a bewitching tone on "Let Her Go", with just a hint of chipmunk.

"That song took me 45 minutes to write backstage at a tiny gig in rural Australia. I thought it was catchy and there was a poignancy to the lyrics, yes, but for it to be a global hit was inconceivable," Rosenberg tells me. "Some songs take months to get right but 'Let Her Go' was so easy. I was no more pleased with it than any other song I'd written. Now it's a hit, I can see why people connect to it. But at the time I was busking and playing to 50 people in a room – I'd never even had a song on the radio. "

Rosenberg, who lives in Brighton and bought a flat on the seafront just before Christmas, near his parents and his new girlfriend, left school at 16. He had learned classical guitar at a young age and started writing songs aged 14. He formed Passenger with Andrew Phillips in 2003 when he was 19 – the five-person band's debut album, Wicked Man's Rest, was released in 2007.

The band broke up in 2009, and Rosenberg went solo and kept the stage name Passenger. He spent time busking in England and Australia, acquiring a small fan base along the way. Then he quietly released Wide Eyes Blind Love (2009), Divers and Submarines (2010), and Flight of the Crow (2011). All of his albums have been self-funded, including Whispers; this time he has licensed the music to Island Records, but he has retained the copyright through his own Black Crow label.

In what he describes as "it's all in the timing", things finally started to click for him in 2012. In 2008 he had met Ed Sheeran – "we were on the same bill in a tiny pub in Cambridge – he was only 16 years old" – and they became friends. When Sheeran became a star he invited Rosenberg to accompany him on his big UK tour, followed by a year or so touring around the world, on and off.

Around the same time, his fifth album All the Little Lights came out and – although he was getting more well-known touring with Sheeran – it wasn't until a Dutch radio plugger heard the track "Let Her Go" in a café that he got Dutch airplay. Within three weeks of the radio exposure, "Let Her Go" was No 1 in the Netherlands. The song spread across Europe and Australia grabbing the No 1 slot – and it was also a top five hit in the US –and propelled his fifth album into the top five in the UK and the top 30 of the Billboard 200 last year.

"'Let Her Go' was there just at the right time," says Rosenberg. "The momentum was building and then it exploded."

Is it stressful trying to write another hit? "There are two ways to approach it – I could pile loads of pressure on myself and think to myself, 'Right, I need another five "Let Her Go" songs in my career, " he says. "Or I think, 'How amazing to have one. What an amazing story to tell my grandkids. What an amazing year of my life.'"

'Whispers' is out now on Black Crow/Island Records