Maybe I'm amazed at being McCartney's chosen guitarist

I thought, okay, when we go on stage, it's gonna be cool. It will be dark. I'll only see the first few rows. I didn't realise that the television lights would be lighting up the whole of Madison Square Garden like a classroom," recalls Californian guitarist Rusty Anderson. "That was a strange experience, but, once I made it through that, I thought 'shit, I can do anything now. Bring it on!'"

The musician is talking about his first live appearance with Paul McCartney at the Concert for New York City, the benefit held a few weeks after 9/11. "It was all about the firefighters. Everyone was trying to get their head around what had just happened," he says of what was a momentous, cathartic occasion. It certainly created an instant bond between the two Brits – McCartney and his long-standing keyboard-player Paul "Wix" Wickens – and the three Americans – drummer Abe Laboriel Jr and guitarists Anderson and Brian Ray. "It fell together in its own organic way and it just works, for some reason. There's a lot of osmosis. We rehearsed once or twice and went up there. It was just nuts. I met so many people that night, Bill Clinton, David Bowie, The Who," he remembers.

Tall, with jet black hair, wearing a dark shirt and jeans, sipping green tea in the atrium at London's Landmark Hotel, Anderson, who turned 50 last year, is as relaxed as can be when your boss is the most famous rock star on the planet. The guitarist had already contributed to several of the most commercially-successful records of the past 25 years, starting with The Bangles' Different Light in the mid-Eighties, when the call came in February 2001, courtesy of that album's producer, his friend David Kahne. He had started work on what would become the McCartney album Driving Rain and "needed some guitar playing." Anderson was thrown in at the deep end.

"I walked into Henson Studio in LA, and met Paul. That was a hyper-buzzy moment. Within half an hour, we were making music. 'About You' is the very first track we did. I started on bass – no pressure there! – and I overdubbed some guitar. We moved pretty quickly. Mostly, for Abe and I, it was about getting acquainted with him, bonding as people," he reflects. "It was bizarre to look over and go, oh my God, there's Paul playing his Hofner bass, and I'm playing guitar. Even though we've been doing this for almost a decade, I still do a double take every once in a while."

Anderson seemed destined to join McCartney's band. "The Beatles were the reason I started playing an instrument. When I was five, my older sister was playing their records and I flipped out on them. The first one I ever got was Help!. My parents bought it for me," he recalls. "I'd steal my sister's guitar and then she'd lock her room, so I got little plastic guitars that you couldn't tune. Then, when I was eight, I got a Kent guitar and amp, a little pawn-shop thing. I'm really passionate about the guitar, it's an amazing instrument. You can bend notes, you can play hard, soft, slide. It's so direct, it's right on your body," he says and proceeds to list the sixties and seventies axemen who inspired him. "Eric Clapton with Cream. Jeff Beck, Mick Ronson, I was really into the Spiders from Mars. The original Alice Cooper band. Frank Zappa. Hot Rats was a pivotal record for me. Through Captain Beefheart, I got into Howlin' Wolf and Skip James, these incredible blues artists."

A precocious and versatile guitarist, Anderson led the bands Eulogy and The Living Daylights before making his name as a session-player in Los Angeles. In the mid-Nineties, as a member of Ednaswap, he made a demo containing a catchy song called "Torn". "We did that in London with Phil Thornalley producing. Natalie Imbruglia pretty much copied the original recording note for note. We ended up doing quite a few versions of 'Torn' ourselves but both Eastwest/Elektra and Island dropped the ball," he reflects without any bitterness.

His guitar has featured on several major hits that have become radio favourites. "A fun one was 'You Get What You Give' with the New Radicals. Gregg Alexander ran out of money so he just threw the demos on the record. He's kind of crazy. He wrote that with Rick Nowels, they did 'Life is a Rollercoaster' for Ronan Keating, and 'The Game of Love' for Carlos Santana. I played rhythm guitar on that," explains Anderson matter-of-factly.

"Sometimes, you go into a session and do a quick thing that becomes the focus of the record, like 'Livin' la Vida Loca'. I came up with a guitar part and recorded it in my home studio with my friend Robi Draco Rosa, who co-wrote and co-produced that for Ricky Martin, The whole thing took an hour and a half. The demo became the record, the first song on the album, the first single. It's funny how that works." The guitarist has also recorded with Stevie Nicks, Jewel and Joe Cocker, but was especially in awe of Elton John during the making of Songs from the West Coast. "Bernie Taupin would have 80 sets of lyrics and Elton would take 15 minutes to turn one into a song. Then we'd just sit around a piano and I'd grab the chords from him and we'd just start recording. Awesome," he can't help enthusing.

Yet, to his well-attuned ears, no one tops McCartney. "He's Mr Melody. It doesn't matter if he's whistling, playing bass or drums. He's always inspirational," says Anderson, letting us in on a few secrets. "Paul has two different modes. One is to just go, to be in the moment. He can be very impulsive. He'll go: 'It's a nice day, let's go rehearse outside.' 'Rinse The Raindrops', the last track on Driving Rain, we jammed for and hour and it was edited down to 10 minutes. It's so free-form, almost a Led Zeppelin vibe. Other times, he'll say, 'I love what you played but I want this specific thing'.

"He's an unassuming guy, very thoughtful, very gracious. He's a polite Englishman. Having said that, he'll surprise you with something out of left field. He likes to keep things fresh. As a band, we've learned to be ready for anything," adds the guitarist who managed to convince his boss to introduce Beatles favourites "Getting Better", "Day Tripper" and "Helter Skelter" to the set list. "Paul has a certain perspective on his own songs," Anderson goes on.

McCartney helped Anderson fix "Hurt Myself", the opening track on Undressing Underwater, his first solo album. "The rescue bit, these are my favourite parts," he recalls the former Beatle saying. "For him, it was exciting. He played bass, a little guitar and sang background vocals. There was a part I didn't know whether to turn into a bridge or edit. He suggested something unexpected, a oboe, a flute or a trumpet. We ended up putting a flugelhorn on there."

Anderson has also contributed to the McCartney albums Chaos and Creation in the Backyard and Memory Almost Full, and the raft of DVDs documenting historic concerts in illustrious settings like Red Square in Moscow. "I get to go to all these places like the White House. Meeting Barack Obama was a dream come true that I didn't really even think I had," he muses. "We played Tel Aviv in 2008. My wife is Palestinian and we met an organisation called One Voice, trying to get the Israelis and the Palestinians together, the two-state solution. The Palestinian issue and the environment are my biggest concerns."

Indeed, Born On Earth, the guitarist's second solo album, is inspired by his travels. "It wasn't intentional but it's loosely about the way technology has affected the planet," he says. "The title track and 'Under A Star' are looking at the planet from a bird's-eye view. There's even a song called 'Baggage Claim'. I look at is as a macro and micro album. There are more personal bits, 'Timed Exposure' fuses the two."

Anderson is rightly concerned about the impact music touring has. "The carbon footprint sucks. I hope we're not screwed. Everything we do needs power. The only solution is to figure out a way to get clean power. I heard someone talking about solar panels out in the ocean. That sounds really smart."

And his advice to budding musicians? "Follow your muse and find whatever inspires you."

'Born on Earth' is out now (Rustyanderson.com). Paul McCartney's 'Up and Coming' tour continues in the US and Canada