Until a few years ago, Peter Bowditch, 70, a retired Royal Mail employee, didn't know what UK grime or drill music was.

When his granddaughter would tune his car radio into stations rap and grime broadcasts, Pete would turn it off. "She was messing with my car radio stations and I thought 'what the hell is going on here?' and I changed them back," he recalls.

But over time, Pete stopped reaching for the dial and began to enjoy what he was hearing. "Then I thought, 'This ain't too bad'," he says. Pete decided to ask his friend, Basil Bellgrave, now 73, if he'd ever considered rapping.

"I thought we'd have a bit of a go," Bas says. Even so, very few would have predicted that the two grandfathers would end up becoming major players in UK drill.

Pete and Bas are both south London born and bred.

Before embarking on a career in music, Pete worked for Royal Mail and Westminster Council. Bas's background is shrouded in mystery - and he likes to keep it that way. As a child, Bas says his father owned a bare-knuckle boxing ring. He has previously claimed to have worked as a lawyer and to have served in the army, while there are rumours he worked as a bouncer in the 1970s. During a previous interview with online channel Noisey Raps, Pete drove Bas around London, where he regularly exited the car to drop off packages.

Asked what he was up to, Bas declined to comment. He said that he worked as a helicopter engineer and a carpet seller.

Asked about the various stories and rumours circulating online about his background, Bas says: "These legends are a bit like Robin Hood aren't they? Some bits are true and some are not. We're a long way from Sherwood Forest though aren't we?"

One part of his story that remains consistent is that he taught piano - and that is how the pair met half a decade ago. Pete walked into a shop in south London "on a little bit of business" and heard the sound of a piano coming from a back room, where Bas was giving a lesson. Intrigued, Pete stuck around and introduced himself.

"We've been lifelong friends... for the last five years," Pete says. It was around this time that Pete, who is a huge fan of The Specials and Madness, was introduced to rap and grime through his granddaughter. He eventually persuaded Bas, a Frank Sinatra fiend, to give his newfound love a listen.

Bas also took a liking the menacing beats and street-smart storytelling of drill, and the pair started writing lyrics in 2017 - bouncing ideas of some of the younger members of the family.

"I talk to my grandkids and their friends and they just let us know the new idioms - what's going on now," says Pete.

"For example, we always thought we were good, then they say sick, they say fire, then they say you're cold, but it all means the same thing." Then Pete & Bas wrote their first song, Shut Your Mouth, which was released on new year's day in 2018.

Within days, it started racking up views on YouTube, while people sought to find out more about these two retired grandads and their blend of modern day and traditional cockney slang. Many thought the song was just a one-off gimmick, but Pete & Bas dropped more songs that year, including Do One and Dents In a Peugeot, as their popularity started to grow.

By 2019 they were releasing songs on major UK rap platforms GRM Daily and Pressplay Media. Both say it was around this time that they noticed a change in the way people were reacting to their music.

"When they first look at it they think, 'This is a laugh, it's a bit of comedy, it's a wind up'," Bas says. "Then they listen to it and they think: 'It's not just funny it's good. It's actually better than a lot of what we've heard'."

Their first live show consisted of around 20 people in a pub in London's Blackheath. By 2019 they were selling out shows across the UK (the tour bus consisted of Bas's campervan) and they even played a show in the party resort of Ayia Napa in Cyprus, where they were pulled over by police while driving mopeds.

"They got out of their car and put their bat under their belt and we thought, 'What the hell have we done now'?" Pete says. "They walked up to us and said, 'Can we have a selfie?'"

Then came 2020 and Covid-19. With both categorised as high risk, the pandemic has been a difficult period for the pair. Pete has lost friends to the virus.

But like many up-and-coming UK rappers, their popularity grew during lockdown. In December, they released Old Estate with M24 - one of the biggest names in UK drill. The genre polarises opinion. With its often provocative lyrics, it's been blamed by police for fuelling gang violence; and drill videos are increasingly being used as evidence in trials.

But its defenders say the genre gives a raw and unfiltered insight into the darker side of life on the country's inner-city estates, and can offer a way for young people to escape the situations they're describing. The image of UK drill rappers often portrayed in the media is a far cry from how Pete & Bas have found them.

"It's very unusual, you wouldn't expect them to be so friendly. They have been very supportive," Bas says. Last month, the stock of Pete & Bas grew even further with their appearance on Plugged In With Fumez The Engineer - one of the biggest platforms in UK drill.

Their performance is already one of the most viewed Plugged In freestyles ever - hitting 5 million views in a month. They now have growing fanbases across Europe, the US, Australia and Japan.

"It does make you wonder what they make of it in Japan, I can't figure it out. But if you want us in Japan we'll be there," Bas says. "We get stopped on the street now. Some of the older men and ladies stop us and say, 'My grandson reckons you're great', and ask for a selfie for their grandson," Pete says.

"It's for them really, innit?" Bas says. But opinion within their own families about their newfound fame is mixed. Pete says he's a "hero" in the family.

"Not quite so much in my family, to be truthful," Bas says. "It's a bit of an elephant in the room, I suppose. I think you're only here once and you've got to make some waves before you go. I think they're maybe thinking it's time he settled down and quietened down a bit."

With lockdown restrictions easing, Pete and Bas have big plans for the years ahead. They have a full UK tour in the works and are in talks with major artists for further collaborations.

"If I wasn't doing music I'd probably be up to no good," Pete says. "The music has changed everything."

"I'd be sitting in my armchair with my feet up the chimney waiting to die," Bas adds. "We're really living life to the full now."