Gilbert and George's postcards from the edge

George, the taller bespectacled half of the artist duo Gilbert and George, is reading aloud to me from one of their new artworks: 'I'll drag you round my posh flat by your nuts you filthy vetch,' he intones in his perfectly enunciated English. Close your eyes and it could be Prince Charles speaking. I can't help sniggering. 'Why is it funny?' asks George, deadly serious. The words are from a collage of telephone-box cards, part of a collection called

I shouldn't be surprised of course. After all, Gilbert and George have become household names in Britain for the way in which they take taboo words and images and present them in the rarefied world of the art gallery. What is impressive, though, is the fact that after more than 40 years they are still finding ways to provoke their audience. For example, when their new show opens at White Cube later this month it probably won't be the telephone- box cards that offend the chattering classes, but the many collages featuring the Union Jack, a loaded image which has lately become a Gilbert and George favourite. 'We think it's the best flag in the world,' says George. 'Taxi drivers like it. People from overseas buy clothes and postcards with it on. But the art world – this so-called educated group – rejects it. Extraordinary!'

The Urethra collection is the first set of new work by Gilbert and George to use collaged postcards since 1989, but their use of the form goes back to 1972 when they exhibited their first 'postcard sculptures' at the Situation Gallery in London. 'Postcards speak,' says Gilbert. 'We were always attracted to them.' In those days the pair would rummage through boxes of vintage cards in London shops, selecting the ones that most appealed to them: photos of London landmarks, portraits of kings and princes, soldiers, gaudy still lives of flowers and parks. These were arranged in abstract patterns that could be read by the viewer in whichever way touched them most. As time went on the patterns became ever more elaborate, culminating in huge works filled with hundreds of postcards of whatever was the most popular theme of the day, including the wedding of Charles and Diana in 1981.

Over the past 12 years Gilbert and George have again been collecting postcards, together with flyers and telephone-box cards. Their rule was to collect any postcard that featured the Union Jack and any flyer or phone card which 'was not boring'. Another rule was that they had to be able to get 13 items the same. This is the number they worked out they needed to form the cards and flyers into a shape approximating the sign for the urethra (a circle with a dot in the centre) which was used by one of their heroes, the theosophist Charles Leadbeater (1854-1934), on all his correspondence. Leadbeater, it turns out, was a great advocate of masturbation in boys, and the urethra – the channel that carries the sperm –was for him a symbol of what he considered this healthy occupation. Once the format was agreed, Gilbert and George were able to make the works fast and almost without thinking – a process they liken to the 'automatic writing' promoted by theosophists. There are 564 Urethra works in all, enough to fill the huge second volume of a new Gilbert and George book, The Complete Postcard Art, which comes out this month.

In 1967, when Gilbert and George first met and began working together at Saint Martins School of Art, it wasn't the Union Jack or the subject of masturbation that caused outrage among the staff and fellow students but their challenge to the prevailing trend for abstract art. 'They were all doing this minimalist stuff – it was all about weight, shape, colour. Real life didn't come into it,' remembers George. This cerebral, disconnected art meant nothing to the two young students who were determined to make work that somehow reflected their own background and experiences of the world.

Both boys, after all, had grown up in rural working-class families where practical concerns came first. George Passmore was born in Plymouth in 1942 and lived with his mother and brother in Totnes until he was in his twenties. His parents were divorced – a scandal in those days – which set him apart from other children. He was an eccentric boy, given to cross-dressing (there is a photo of him in a skirt and flowery hat at Totnes Carnival in 1951). He left school at 15, but enrolled for art evening classes at Dartington Hall where his interest in the subject blossomed. Gilbert Proesch, meanwhile, was born in the village of San Martino in the Italian Dolomites in 1943. His father was a shoemaker and young Gilbert learned to use tools in the family workshop. He soon became an expert woodcarver, honing his talent on images of the Virgin and saints. He left home at 17, travelling first to Austria to study, then to Munich, and finally to London where he enrolled at Saint Martins aged 24.

When the pair met on the Advanced Sculpture course George remembers that 'it was love at first sight'. Photographs from the time show Gilbert as a particularly handsome boy, with fine features and dark, piercing eyes. As well as being homosexual (a word they don't use about themselves, preferring to describe everybody as 'sexual'), he had the added attraction for George of being foreign and exotic, and therefore a kindred outsider. The two became insep-arable and quickly began to formulate the idea that would be their greatest achievement: to devote their entire lives to becoming living sculptures.

From this key moment in Gilbert and George's career, everything else flows. In order to stand out they did the opposite to what was being done by every other artist of their generation. They began to wear formal suits every day, at a time when George recalls other students wearing 'bell bottoms and platform shoes'. They embraced old-fashioned values of courteousness and formality, making 'postal sculptures' on embossed cards and collages of vintage postcards featuring the Royal Family. They set out The Laws of Sculptors, which began: 'Always be smartly dressed, well groomed, relaxed, friendly, polite and in complete control.'

Most memorably of all, in 1969, they painted their faces bronze and performed the music-hall song 'Underneath the Arches' in art schools around London (evocative footage of this is now on YouTube). It is a mark of the originality of this work that the pair were soon being courted by the smartest galleries and, in 1970, were invited by David Sylvester, the most famous critic of the day, to make a 'magazine sculpture' for The Sunday Times. In the published text, Gilbert and George described their lives: 'We are only human sculptors loving nightly tea drinking looking encouraging life fighting boredom dying very slowly greeting politely and waiting till day breaks.' They signed the piece and added the motto 'Art for All'.

Forty years later it is remarkable to discover how consistently they have stuck to these early principles. They still live in the same East End house in Fournier Street that George moved into when it was a derelict wreck in 1968 and which they bought together in the early 1970s. The Georgian houses on this street are now wildly expensive (Tracey Emin lives across the road), but when the pair first came here it was an area for immigrants and the dispossessed, far away from the fashionable arty centre of Chelsea. George answers the door and shows me down a long passage filled with shelves of Victorian glass and out across a small yard to a large, tidy studio where Gilbert is waiting. We pause on the way to admire a salvaged drinking fountain engraved with the words 'Jesus said if any man thirst let him come unto me and drink'. 'Extraordinary!' says George. 'You would never be able to have that in public now, would you?'

We sit down at a long table to talk. George is wearing a green tweed suit, Gilbert a matching one in brown. They both have Parker pens in their top pockets. They wear different ties: George's is covered in images of their work and Gilbert's is patterned with a street map of the East End. At first there is something unnerving about sitting opposite two men dressed the same, with their formal manners, George's 1950s English and Gilbert's Italian-accented speech. But they smile and laugh a lot, which is reassuring. I say how impressed I am that over the years they always seem to have spotted exactly the subject that will most irritate the critics and gallery-going public and therefore elicit a response. In the early 1970s this began with photographs of themselves getting drunk (not con-sidered high-brow enough for art in those pre-YBA days), and soon moved on to large multi-panelled photographic works of London street scenes, most famously The Dirty Words Pictures of 1977, in which graffitied expletives such as 'Fuck' and 'Queer' appeared above their self-portraits. It is an indication of how both art and times have changed that those works now seem less confrontational than Gilbert and George's most recent pictures, the huge colourful compositions that feature Muslim teenagers, Arabic script, newsstand posters announcing the London bombings, and words such as 'Hooded'.