Any Londoner well-versed in Tube etiquette knows the unspoken rules - head down, eyes fixed forward, disregarding the stranger nestled snugly beside you. But Bob Mazzer takes a different approach.

For 40 years, the photographer has travelled the length and breadth of the London Underground, documenting all he witnesses.

He has captured candid moments, building up a social history mapped by fashion, hairstyles and changing attitudes to smoking and drinking on trains.

Now the 65-year-old has collected a selection of his favourite images together in a new book Underground - in his words, where "the very intimate meets the very public.

"I've always found the Tube a fascinating place to be, ever since I was a kid at school," Mazzer adds. "It's just this amazing confluence of people and engineering. And I am interested in both."

Born in the Royal London Hospital in Whitechapel, Mazzer grew up in Manor House, next to the Bernhard Baron Settlement - an area of tremendous social change for Jews in the 50s and 60s under the reformer Basil Henriques.

He received his first camera for his barmitzvah - "a little plastic tin thing" - and immediately started documenting the faces and places around him. But it was not until his later teens that he decided to take up photography as an art form, eventually studying at Hornsey College of Art.

"I was never really interested in making a living out of it," he recalls. "As an artist, you just have this voice inside you telling you 'this is meaningful - take the picture'. I think the camera is the best tool for explaining man to himself."

For a while, photography remained a hobby while he led an "alternative lifestyle" in Wales. "That was most definitely not a Jewish area," he says. "We were a bunch of hippies sitting on a rooftop."

Mazzer supplemented his passion with odd jobs including harvesting Christmas trees and working in an animal feed factory.

It was only when he returned to Manor House and took a job as a projectionist at an adult film cinema in Kings Cross that he truly began to use his camera as a constant recorder of everyday life.

"That job was an amazing education, just from the kinds of people you would see turning up and leaving. I would travel home late every night on the Tube and witness this amazing party feeling on the platform, and without really thinking about it I just started to take pictures. I was also able to build a darkroom with the money I made."

For Mazzer, the Underground has always served as a fertile source of inspiration, capturing the human condition at all extremes and unsuspecting moments.

"You can see people down there smooching, kicking off, or just being totally nonplussed," he says. "There isn't a lot of space between you and the next person and you can't get away. It's a place where we all get squashed together and we just have to put up with it."

He has met his fair share of colourful characters down the years. But he has rarely felt the need to censor his work, or turn the camera away from a scene.

"I like to engage with people and unless there was something obviously private going on, I would regularly approach them and ask to take their photograph. You can normally tell who wants attention.

"And you all become part of the same herd, sharing that very intimate environment. There's a closeness between you. But then, of course, you're released back into the wild, never to be seen again."

Bob Mazzer's Underground is published by Spitalfields Life. His exhibition is at Howard Griffin Gallery, 189 Shoreditch High St, London E1 until July 13