When Jeremy Cooper was a cash-strapped history of art student in the late 1960s, he hitchhiked around Italy collecting postcards from every church he visited. At the time, full-colour illustrated books were beyond his means, so the postcards were an inexpensive way of collecting high-quality images of 14th-century Italian art. His fondness for postcards remained and decades later, while he was working as an antiques dealer, he started to notice a large body of work that had never been fully explored: postcards created by contemporary artists.

Over the past 10 years, Cooper has been collecting postcards made by artists ranging from Yoko Ono to David Shrigley, Joseph Beuys to Marina Abramović, Gavin Turk to Gilbert & George. “The more I looked, the more I discovered that it’s a field of unrecognised historical significance – it just seemed completely neglected,” he says. “These postcards were made by artists as individual expressions, not just the reproduction of a work of art, which is what most postcards are.”

The project was largely born out of Cooper’s antagonism to the huge sums of money involved in art collection. Formerly an auctioneer at Sotheby’s, Cooper quit the job after becoming disillusioned by endless discussion of how much a piece of art was “worth” (he left the BBC’s Antiques Roadshow for similar reasons). “I just didn’t want to be a part of it,” he recalls. “I think millions of pounds per work of art is grotesque, when there are loads of people finding it difficult to eat.”

In that same civic-minded spirit, Cooper has donated 1,000 of the postcards he collected to the British Museum, where they will be exhibited next month; more than 300 of these are collected in a book charting their evolution from 1960 to the present day.

Gilbert & George, 1972. Part of an announcement by the Arts Council for the show The New Art at the Hayward Gallery, London, 1972.As a number of the artists in this significant exhibition (Gilbert & George, Keith Arnatt, Richard Long, Hamish Fulton, Art & Language, Barry Flanagan and others) had been students together at St Martin’s School of Art, London, in the mid-1960s, the Arts Council decided to put one of the group’s works on the postcard invitation, choosing Gilbert & George’s Photo-piece (1971). Photograph: Reproduced with permission of the artists

The format of the postcard, says Cooper, has been appealing to a variety of artists owing to its low production costs, versatile size and shape and the ease with which it can be distributed. For these same reasons, postcards are often used for political messages and attract artists with an interest in disruption and subversion: Peter Kennard’s anti-war postcards are included in the book, as are feminist works by Zoe Leonard and the activist collective Guerrilla Girls (one postcard titled “The Advantages of Being a Woman Artist” includes reasons such as “work without the pressure of success”).

Yet, within the confines of the format, the finished works differ wildly: techniques include screen printing on to the cards, creating collages out of them, scratching out holes or simply scribbling on top with a felt-tip pen. Some were made in large quantities, others are editions of one; some are manipulations of found postcards, others are entirely original works of art. Most were actually sent in the post, including one from 1969 that Jasper Johns sent to an art dealer as an invitation to his show. “He just gave it away. I mean, it isn’t given away now, I can assure you. But a Jasper Johns painting [would cost] $20m – this [would be] £350 and it’s a lovely thing.”

Unlike much collectible art, Cooper stresses, postcards are affordable – most of his cost less than £100, with the most expensive around the £5,000 mark. He was also given a number of items from artists such as Tacita Dean and Rachel Whiteread, who were happy to help out when they heard about his project.

“It’s possible to form a significant collection of extremely good and important works of art without being wealthy,” he says. “Anyone could decide to form a collection very close to mine with most of the same things – and I like that. It’s anti-exclusive.”

The World Exists to Be Put on a Postcard: Artists’ Postcards from 1960 to Now by Jeremy Cooper will be published by Thames & Hudson/the British Museum on 7 February (£19.95). A free British Museum exhibition runs from 7 February to 4 August