When Ewan McGregor, Jonny Lee Miller and Robert Carlyle shot to fame with Trainspotting – so did Lorenzo Agius, the photographer who took the film's iconic black-and-white publicity shots.

A year later, in 1997, his photograph of Liam Gallagher and Patsy Kensit defined Cool Britannia on a Vanity Fair front cover. It is, says Agius proudly, the only time the magazine's legendary cover has been shot by a photographer on their first shoot. Since then, he has regularly photographed A-listers from Angelina Jolie and Brad Pitt to Beyoncé, often capturing them in unexpected ways with his characteristic naturalness and quirky humour.

From 14 September to 14 October, a selection of his images will be on show at the Alon Zakaim Fine Art gallery in London's Mayfair. There is Jack Nicholson jumping, Jude Law and Ewan McGregor having breakfast in bed together, Madonna eyeballing a mouse and many others. His intimate images capture the essence of his subjects. "With Ewan as Renton [in Trainspotting], you can see what he's like and that he's suffering. He is going cold turkey and he's lost," Agius explains.

For Agius, the best shots are those which are spontaneous, because they happen so rarely. For example, Jack Nicholson jumping in the air and clicking his heels as he and Agius were talking about Fred Astaire or Sienna Miller creating a moustache as she relaxed in a bath. "We were drinking, smoking and fooling around. I was shooting Sienna around the bath with one foot on the side – a real Blow Up moment. And suddenly she made a moustache with her wet hair."

Other unplanned elements can also work well as they allow the personality of the actor to emerge. Agius recalls a shoot with Hugh Jackman on the roof of a hotel in downtown Los Angeles. "Suddenly, Hugh started to climb from the roof onto the metal signage high above the street. His publicists were freaking out but he's an action man so I let him do it," he says. Agius isn't afraid of provoking his subjects, either. "Carlyle was so aggressive as Begby in the film [Trainspotting] that I wanted it to come through in the shots. It was like a screaming match, a frenzy. He was opening beer cans and spraying them everywhere until we were both covered in it. I was screaming at him. So he stuck his fingers up in the V-sign that made the shot."

He also pushes the boundaries of his stars. For example, the shots of McGregor and Law in bed together. "Jude didn't want to do it at first because he was worried about how he would be portrayed, but he agreed after I said, 'Let's channel Morecambe and Wise,'" he recalls. "For the shot in the bathroom, I couldn't stop them laughing. Jude pulled his trousers and pants down and sat on the toilet reading the newspaper, as Ewan stripped off naked and got into the bath. It was as if they were an everyday couple," he says.

Agius likes to bring out a different side to his stars, too. Describing his shoot of Madonna around the time she published her first children's book, The English Roses, he says, "I wanted to capture her softer side, as the writer of children's books, rather than her usual strong, masculine images. At first, it was difficult for her to be herself. It looked like she didn't know what to do but when I gave her directions such as lean against the bookshelf with her legs in the shape of an M, she started to relax and let her personality come out."

He also tries to reveal a private side of the celebrity. "My shot of Tom Cruise, relaxing in his chair is just like a picture of you or I. He's in a private moment of reflection. It is all about what's behind the eyes and in the head. Suddenly, he connected to something and opened up. You can see the connection in the eyes," he explains.

Gaining trust is crucial. It allows him to capture natural moments even in sensitive times. His shot, for example, of Kiefer Sutherland on location for 24 shows the actor with stitches in his head after one of his infamous bar brawls. The TV cameras had to film around him until his face healed. "He allowed me to shoot him because we have developed a relationship over the years. No one likes being photographed. It's time consuming and they may not know the photographer and lots of photographers can be a nightmare. So it's good to work with someone you know".

For Agius, the image portrays Sutherland as he is. "He's a regular, real guy. What you see is what you get. He's not aggressive, but with a few drinks, he may want to punch someone's lights out."

In other shots, the relationships between stars and their fans are laid bare. He remembers following Eric Cantona around Marseille for three days, taking pictures for his autobiography. Every time Cantona got out of the car, dozens of kids would turn up and watch his football tricks, mesmerised. "It was interesting to see other people's reactions," says Agius.

One of his most bizarre shoots was with Nicholson at the Beverly Hills Hotel when Victoria Beckham was co-styling. "Jack wanted to meet her. She was a fan of his. We were in the master bedroom. Victoria was sitting at the end of the bed in awe of Jack who is standing there in his boxer shorts and no trousers [he was having a fitting]," he laughs.

Sean Penn and Philip Seymour Hoffman are the two stars whom Agius has yet to shoot and would most like to. Penn because he's "deep and interesting" and Hoffman for his "intriguing, yet vulnerable" air.

For Agius, the most important thing is to make the shoot real. If it's been jokey and fun you can see it. It translates into the final images.