Talking at his offices in London's Marble Arch, he is dressed more for comfort than impact, in faded jeans and a grey knitted cardigan. He rests one foot on a coffee table and leans back into a plump sofa, as he eases into a number of recollections from those glory days when, to quote a friend of his, former editor Robin Morgan, "Terry was the go-to guy" for images of the world's rich and famous.

"It was a bloody joke," he's fond of saying in his working-class cockney accent, sounding not unlike English actor Caine, as he describes an accidental meeting with the great train robbers, or being asked to shoot the Beatles while they were recording their debut studio album, , at Abbey Road, in London, one of his first professional assignments.

"I didn't know what I was doing, really. I just asked Ringo [Starr] to hold a cymbal," he says, with a self-deprecating chuckle.

"No one had ever photographed a pop group before so I could get away with anything. I just did what I thought a pop group should look like."

His photograph of the Fab Four was the first image of the group to appear in a national newspaper.

In those days, O'Neill was a novice, learning his trade at Britain's tabloid newspaper. Though naturally a shy man, he was by no means intimidated by the likes of the Beatles or the Rolling Stones.

"They were unknown then," he says, "and, if anything, they looked up to me because I was the photographer who could get their picture in the papers."

O'Neill admits he was lucky to "start at the top" in the world of photography, but his ambition back then was to be a jazz drummer. He played at United States Air Force bases and jazz clubs in and around London, before applying for a job as an air steward with the British Overseas Airways Corporation (BOAC; later British Airways). He had hoped to use his off-duty periods in New York to play in clubs there, too.

Instead, BOAC offered him a position in their technical photography department and, reluctantly, O'Neill took the job.

"I stumbled into photography," he says. "I still used to take the whole drum kit - bass, snare, cymbals, everything - all on the bus to Uxbridge, where [my band had a regular contract to perform]. It was the No222 bus. I will never forget that bloody number."

Would he prefer to have made it as a drummer rather than as a photographer?

"Oh, no, no," he says, emphatically.

"I used to go out with the Beatles and the Rolling Stones - we used to meet at a little place called the Ad Lib Club, in [London's] Leicester Square, and joke about what we would all do for a proper job when the 60s were over. I used to think, 'Thank God I'm a photographer because who the hell would want to be a 60-year-old drummer?'

"None of us thought it could last. We used to joke about Mick Jagger still singing at 40 years old. Now look at him," says O'Neill, with an irreverent smile.

The Rolling Stones frontman is featured twice in O'Neill's forthcoming exhibition, at the Picture This Gallery, in Central. The only other subject to be featured in two images is American actress Welch.

"Raquel was always someone I could work with, because I had worked with her when she was starting out. I went to the filming of [1966 movie] and she was a really sweet girl," he says.

Their friendship has lasted more than 30 years.

"She told me she thought she'd be crucified her whole life for wearing that fur bikini in the movie and I thought, 'That's it - I'll crucify her.' They set up a full-size crucifix at the 20th Century Fox studios and I did the picture."

The resulting image is unforgettable, but it wasn't published until three decades later, in the .

"After the shoot, I got nervous as I was brought up a Catholic and feared people might think I was insulting Jesus Christ, so I didn't publish it until the year 2000," says O'Neill, whose parents were Irish immigrants.

It was while on assignment in the US shooting Welch that O'Neill met Ava Gardner on a film set. He mentioned the possibility of working with her ex-husband Frank Sinatra.

"Ava was very nice and she wrote me a letter to give to Frank. I don't know what she wrote but whatever it was, it opened up a door for me and I was with him for the next 30 years, off and on," says O'Neill.

He recalls arriving at Sinatra's Miami hotel and having no idea how he would get access to the legendary singer, even with the letter of introduction.

"I just didn't know how to go about photographing Sinatra at the hotel or what was the best way to approach him. He suddenly appeared around the corner of the boardwalk with his bodyguards and I just captured the moment," he says.

It was his first image of Sinatra and it is considered his best. Sinatra is seen with his entourage walking along the boardwalk, complete with a body double dressed in an identical suit and a huge security guard.

"He was truly a great man. He was a one-off and a really great musician," says O'Neill.

And it was those early days with Sinatra that taught him the secrets of his trade.

"That first time I met him, in the 60s, he taught me what photography was all about. After three weeks with him, I worked out what a gift he had given me - I realised the secret was getting into someone's life," says O'Neill.

It was his talent for accessing his famous subjects' lives without becoming part of them that gave O'Neill his unique photographic perspective.

Being intimate for long periods with very famous and magnetic personalities, often with extremely lavish lifestyles and huge egos, meant O'Neill had to learn to blend into the background and develop an instinct for knowing when to leave.

"You need to use your loaf [head]," he says. "I had to learn to know when to be around and when not to be around. You just learn to disappear when you need to."

And with Sinatra, O'Neill admits, he nearly lost his way, like a moth drawn too close to the flame of the singer's charismatic presence.

"There came a time with Sinatra when a friendship developed and he wanted to go and have a drink or something. I used to go to the prize fights with him and then I realised this was all wrong. I was being photographed with him and I was supposed to be taking the photos. I have a lot to thank Sinatra for in my life, as he taught me every major lesson about photography, but I had to just back away," he says, and, for a moment, his easy-going, affable mood falters slightly.

"For a while there was this stand-off and I think he just realised that I might be better off as the photographer rather than his best friend. Yes, it was difficult. It was awkward. I had to really think about it but, in the end, I just had to brazen it out."

Despite being part of the swinging 60s scene, O'Neill never became entangled in the drug and alcohol-fuelled hedonism associated with that era.

"Thank God I did the job I did," says O Neill. "I could easily have drifted off with the Beatles or the Stones but I had to be at work at 8am every morning developing images, so I just couldn't be up all night getting drugged off my head."

Though, he admits, there was pressure to conform.

"I did try marijuana once but it didn't agree with me. I even tried cocaine once but it's not for me. I thought I had to try it as people just got on to you about it," he says.

Handsome and successful, O'Neill became famous in his own right. In 1983, he married Dunaway, one of the most glamorous actors of that time. Yet he avoided becoming engulfed in the fantasy world of Hollywood.

"Oh, I hated that," he says, referring to the fame and attention.

"I hated being married to Faye. I made a mistake there. I should never have married a movie star. I always said I never would and then I did. Everyone looks at you and judges you. I liked to hide behind my camera. I was happy there and I avoided the spotlight. I could never stand up and give a speech or anything like that. I was always happy just being in other people's lives and I like to let the pictures talk for themselves."

While O'Neill's work can be found in more than 30 prestigious art galleries around the world, he still considers himself to be a journalist rather than an artist.

"I started out on a newspaper and it was the best training I had. I always wanted my pictures to tell a story," he says.

In 2007, he founded the annual Terry O'Neill Award to encourage photojournalism and protect the industry.

"I want to keep it alive," he says. "Some of these guys risk their lives and there is just nowhere to publish it anymore."

O'Neill is not a fan of digital photography.

"Now I go to a film premiere and the press photographers get the celebrities to stop and then they just hammer off 30 shots and hope they have a good one. That's not photography, that's a joke. It's supposed to be about capturing a moment. I used to go into Paul Newman's life for weeks at a time and I was made welcome," he recalls.

Nor does he like powerful PR and management companies that insist on sanitised and digitally enhanced images of their pampered celebrity clients.

"Say I wanted to go and shoot Tom Cruise, for example. Now, his PR company would tell me what images I could use and demand copy approval and insist on digital retouching. I have never retouched an image in my life. I never needed to," says O'Neill.

"To be honest, there is no one I want to photograph any more. I really wanted to photograph Amy Winehouse, as she would have been a great jazz singer. I worked with Elton [John] and all the big music stars but I think it's all over now," he says.

The man who has photographed hundreds of beautiful women, from Brigitte Bardot and Audrey Hepburn to Kate Moss and Naomi Campbell, does not think much of the latest crop of supermodels, either.

"What's she called … that latest top supermodel?" he asks and is prompted by one of his young assistants.

"Cara Delevingne?"

"Yes, that's her, Cara Delevingne, I just don't rate her," he says. "If she's a supermodel, then I'm King Kong."

O'Neill's early images reflect a golden era, when the counterculture (think mods, rockers, flower power) encouraged young people to challenge established ideas and conventions, often via fashion, music and art, and the women's liberation movement gained momentum, partly due to the introduction of the contraceptive pill in 1961.

Morgan says that era gives his friend's work a poignancy today.

"Terry captured a time when the youth of that era were emancipated," he says. "The technology for that time was guitars, cameras, pens and the hairdresser's scissors but now they are using the technology of today. They are using those tools to say, 'Wake up, listen to us, we have a voice.'

"Kids are protesting against the establishment again using smartphones and social media at G11 summits, on the streets of Hong Kong, in London and New York."

These days, O'Neill seems more sentimental than political and is enjoying promoting his work at international exhibitions, travelling the world by air, as he dreamed of doing when he applied to BOAC more than 50 years ago.

It is astonishing how a man who has been immersed in such a capricious and superficial social orbit for so long, has remained so down to earth. He is an amiable fellow, with a dry, self-deprecating sense of humour, who is as happy discussing football (he's an ardent Chelsea fan) as he is superstardom.

"I've never been in awe of anyone really. I appreciated all the help those famous people gave me and all that, but I have never lived off it or anything," he says.

Perhaps it is that detachment and ambivalence about being in the spotlight that has allowed him to achieve such intimacy with so very many famous people and earn their trust. He was always in their presence as a professional photojournalist, never as a competing personality or rival ego. He never sought their friendship, though so many felt comfortable to offer him theirs.

O'Neill ensured it was always about them, not him. That was the secret that allowed him to get so close to his subjects and capture timeless, iconic images that reflect another age.