IT IS not often that one finds a photographer whose work spans 50 years, possesses eloquence, grace, drama and visual wit and has not been seen before. Colin O’Brien is one of these rare discoveries, an amateur with a remarkable eye for the world around him.

His first proper show, at the.gallery@oxo, gives us 50 black-and-white photographs, all of them urban landscapes that explore the strange conglomeration of people, places and events that make up the society of ordinary London.

Since the age of 10, when his uncle showed him how to develop a photograph, O’Brien has drifted with his camera, without any particular agenda, capturing tableaux, finding anecdotal detail, collecting his visual treasures. He has worked mostly in poor neighbourhoods because they provide a street life that is sociable and visually interesting.

There are few unusual happenings in his photographs; most of them show the games of children, the errands and conversations of the middle-aged, and the observant waiting of the old. But what is remarkable is that these routine acts of life are revealed as being full of humour and pathos, as if the street were a stage and its people were actors, mimics and dancers.

Three thrifty ladies in their best hats and coats peer into the window of Solmans, a second-hand furniture shop, in 1963, their body language betraying the excitement of a bargain spotted. Mrs Leinweber, a neighbour of O’Brien’s, pauses at her Clerkenwell kitchen table in 1959, calculating how she will eke out one more portion from the shepherd’s pie she has made for her 12 children. The cups on the table are chipped, the furnishings modest, but the place is clean and arranged with pride. It reminds one of Bill Brandt’s portraits of a miner and his wife, or of Thurston Hopkins’s work for Picture Post in the 1950s.

Like Roger Mayne, who also photographed the London poor in the 1950s and 1960s, like Brandt too and even Cartier-Bresson, there is an undeniable empathy between O’Brien and his subjects. But what also links these photographers is that they took their best pictures not for magazines, books or gallery walls, but simply for themselves.

Without deadlines or editorial demands, without any constraints, they were free to document the world their way, searching for slices of fact that, when laid together, form their own personal fantasy.

O’Brien’s work is structured with a classical sense of composition and a powerful implied narrative, neatly resolved. One of the finest photographs, taken in 1960, shows a boy dressed as a cowboy, a Stetson on his head and a plastic shotgun in one hand, comforting his young “girlfriend” as they walk along the pavement. The picture distils a particular moment in time, giving you all you need but also making you want to know more. Did the boy scare the girl as he thundered by on his imaginary horse? Are there other cowboys from whom he is protecting her?

Another shot, taken in Brighton in 1959, witnesses an old lady walking under leaden skies along a dreary road beside a building site. She carries a huge basket packed with bunches of fresh flowers wrapped in paper. Although the photograph is in black and white, we can still see the incongruous vitality and exuberance of her load in contrast to the glum drabness of her surroundings and the weariness of her expression.

You might look at these records of how things were in English urban neighbourhoods 50 years ago and wonder what has happened to the quality of common life. Children can no longer play safely on the streets, but in O’Brien’s recent photographs you see that women still gossip and console, the elderly still watch and wait, the young still flirt. The street life is still there and it is still richly entertaining.

Another photographer who finds an alternative world in the familiar streets of London is Leila Miller. Her colourful nocturnal photographs, leading us into a mysterious twilight fantasy, show a fascination with texture and grain.

Wandering through her neighbourhood, she focuses on the contrasts between materials, finding rich detail in the most unexpected places: the stitching on leather suitcases shot through a shop window; the grain of suede running shoes on grass; smooth conjunctions of polished steel. They are all washed with the strange, velvety light of street lamps and provide us with unusual epiphanies.

• Colin O’Brien: Retrospective Images 1954-2004 is at the.gallery@oxo, SE1 (020- 7401 3610) to Sept 5. Leila Miller: We Live As We Dream is at Adam Street Club, WC2 (020-7379 8000) to Sept 4