The Brian Wilson of 2011 cuts a very different image from the one who carved out such glorious, sun-kissed music with The Beach Boys.

In those halcyon days of the mid-Sixties he, along with younger brothers Dennis and Carl, cousin Mike Love and school friend Al Jardine (among other band members that came and went) took the sounds of America’s West Coast and their heavenly harmonies around the world.

During the latter part of that decade, the serious mental-health problems that still plague Wilson began, brought on by his Herculean drug intake and exacerbated by the pressure the band were under at the height of their Beatle-rivalling fame. Add to that rumours of a stroke at some point and he’s not in the best shape.

One subject that illuminate Wilson, who turned 69 on Monday, the music of George Gershwin.

There are many parallels between Gershwin and Wilson — both fused American contemporary culture with classical symphonic arrangements to rewrite the rule book, both worked with their siblings and both, for different reasons, burned out early.

“My favourite music is George Gershwin, doo-wop songs and Phil Spector’s recordings,” he says. “I don’t listen to modern music. New music is a bunch of baloney.”

Wilson has long been fascinated by Gershwin’s compositions, and first heard Rhapsody In Blue at his grandmother’s house when he was four and vaguely remembers loving it. It wasn’t until he was 28, however, that he heard it again and fully appreciated the majesty of the music.

“When I heard it that second time I thought, ‘I’m going to learn that’,” he says. “I worked it out four notes at a time, and ran backwards and forwards from the record player to the piano. After two weeks, I finally had it down and learned to play it.

That’s impressive when you take into account Wilson being deaf in his right ear.

“I’m looking forward to people hearing this album,” he adds. “It took two months to record.”

The album, Brian Wilson Reimagines Gershwin, is out now and features new arrangements of Gershwin classics.

On paper, the thought of these jazz standards being given a Beach Boys-esque makeover might not sound particularly appealing, but there’s something strangely compelling about the playful, hugely affectionate new versions, while two songs — The Like In I Love You and Nothing But Love — are based on previously unrecorded music written by Gershwin.

Wilson says: “We just used a few of the chords, but it’s not similar to how he did them at all. We just took a bit of the song and extrapolated on it.”

The album came at the end of a lengthy creative dry spell for Wilson. Before writing the new arrangements, he hadn’t written a for four years.

“I’ve not written in so long. I sit at the piano but my hands don’t want to do it. ‘What the hell’s going on here?’ I say, ‘Come on Brian, I know you can do it’, but nothing comes out. Then I get a spark, but I can’t understand why I’m having such a dry spell.”

Of course, he’s written more than his fair share of hits already — God Only Knows, Good Vibrations and California Girls to name three of the most famous songs of all time.

In September, Wilson and his band return to the UK to perform the Gershwin album, as well as one or two Beach Boys hits. If his previous performances are anything to go by, they’ll be extremely special evenings.

In 2002, Wilson came out of virtual retirement to perform Pet Sounds in its entirety. Now, live performances of albums are commonplace, but 10 years ago, no-one was doing it. Wilson is still an innovator.

“I was worried to death that people weren’t going to like it and it wasn’t going to go over. But it went over so well,” he says.

On the night of his first performance at London’s Festival Hall the auditorium was full of people crying their eyes out at the beauty of what they were seeing and hearing.

Here was a man so frail he was helped to the stage, reading between-song chat from an autocue, but seemingly coming back to life as soon as he started playing his piano.

The effect was repeated in 2004 when he performed lost classic SMiLE for the first time — an album he started working on in 1966, but didn’t finish and release for 38 years — and again in 2007 when he played That Lucky Old Sun, a collaboration with old friend Van Dyke Parks.

It’s unlikely Wilson will make another album — “It’s so much work” — but he does love performing.

It’s the opposite of his stance in the Sixties, when he retired from touring with The Beach Boys, staying at home to write and record new material.

“I feel I can sing now,” he says. “And I feel comfortable on stage. I feel I can sing God Only Knows the way Carl would sing it, or Surfin’ USA like Mike would. I feel happy on stage. Happiest of all.”

* Brian Wilson will be at the Bridgewater Hall, Manchester, on September 13.