The Beach Boys cast a ray of sunshine over the 60s music scene. Formed at high school in Hawthorne, California, brothers Brian, Dennis and Carl Wilson teamed up with cousin Mike Love and childhood friend Al Jardine and went on to become one of the most influential bands in pop history. 'We started on a hope and a prayer,' explains guitarist and co-founder Jardine, who also sang lead vocals on some of their biggest hits (including 'Then I Kissed Her', 'I Know There's an Answer' and 'Help Me, Rhonda'). 'In fact I had to rent the instruments because we didn't own any at the time, but when we sang together we knew we had a pretty good blend. We had no idea it would turn into 100–200 million records [some estimates put their sales as high as 350 million], it wasn't supposed to last at all after that first record.'

The group were inspired by doo-wop, 50s girl groups, Mel Tormé, the Ink Spots and even Roy Rogers. 'It's simple, it's complicated and everything in between; it's barbershop, jazz and folk, it's pretty much everything, it's hard to define,' says Jardine. 'We created our own unique formula. Brian had this ability to articulate and hear harmonies that most people don't hear, so that helps, and then you have the messengers, the Beach Boys, who delivered.'

They found their niche singing about summer holidays, beaches, parties and, of course, surfing, with their early hits playing up to California clichés. Then 1966's Pet Sounds changed everything. Chief songwriter Brian Wilson was reaching for something bigger and more complex – a trip into the psychedelic end of pop with multi-layered harmonies, found sounds and extensive use of the Theremin. It's a more personal album and a labour of love for Wilson. And it's still considered by many to be one of the greatest albums of all time.

'It continues to resonate because it is just so profoundly simple and relatable. It's multi-layered production and good quality songwriting just makes the whole complete. All those elements together, those arrangements, it's a phenomenon.'

credit: © Capitol Photo Archives

The protracted recording sessions also took their toll on the band. 'I remember two songs in particular which took the longest and were the most difficult – "Wouldn't it be Nice" and "Good Vibrations" – we expended months of energy perfecting them. They were both going to be on Pet Sounds but as it turned out, "Good Vibrations" didn't make the grade. Brian insisted on holding it back for the next album because he thought it was too advanced. It's probably the worst decision he ever made,' says Jardine with a wry chuckle.

These mammoth recording sessions stretched on for months. Not only recording Pet Sounds but also working on its mythical follow-up Smile. In many ways it was the beginning of the end of the classic lineup. 'Oh yeah majorly, majorly physically, emotionally, creatively taxing,' admits Jardine. 'And expensive I might add. I don't think we'll ever know how much it cost but I did hear "Good Vibrations" had a $60,000 bill by itself and that's a lot of money back in the 60s.'

Brian stepped away from touring to concentrate on ever-more complex recording projects, most of which never saw the light of day. He struggled with agoraphobia, drink and drugs, withdrawing from public life. Then in the 90s and 00s, Wilson gradually began to resurface, working on new material, touring and finally releasing Smile in 2004, 37 years after he had first started working on it.

Jardine rejoined Wilson on the road in 2006. 'His wife called me and asked if I'd like to come back, give it a try with the band, he needed a little shot in the arm and our friendship is strong and non-threatening.' Brian contributed vocals to Jardine's solo album A Postcard From California and they have been playing together ever since. Jardine returned the favour appearing on Wilson's most recent record No Pier Pressure in 2015 alongside Blondie Chaplin who has been playing with the Beach Boys since the 70s.

It's nice, too, to hear from Jardine that relations between the original Beach Boys are less fractious than the media would have you believe. 'We got together a few nights ago at Capitol Records and there was no enmity at all, just a lot of respect,. Unfortunately managers and agents all have competitive spirits so it often looks worse than it is. I'm hoping we can all get together for one last bash and do some shows.'

For the capital's Summer Sessions concert series, Wilson will be joined by Jardine and Chaplin and unsurprisingly their set will concentrate on Pet Sounds alongside other Beach Boys classics. 'I never expected it to last this long,' says Jardine. 'It's a testament to the songwriting; a group of guys who stumbled forward and never quite knew what we were doing.'

Brian Wilson presents Pet Sounds, Playhouse, 19 Aug, 7pm, £50--£85.