For Peter Kennard, the politics came first. Originally training as a painter at the Slade School of Fine Art, he was radicalised by the explosive events of 1968 and turned to photomontage to get his message across. "You can spit on them, you can jump on them, but photographs take you back to the subject and the moment the image was taken," he says. "Photography is key to what I do."

Outraged by inequality of weath and the arms trade, Kennard's images over the years have shown Poker players using warheads as chips, combine children's faces with Financial Times markets tables, morph skeletons with mushroom clouds and - most famously - personify the globe into a gas-mask wearing, warhead-eating face. For Kennard, bringing together these seemingly disparate images links what are actually closely interrelated problems, and chips away at the carefully-controlled image of the world promoted in our highly mediated culture. "We are all bombarded by images selling us things we don't want or need," he says. "Montage is used a lot in advertising but for me what's interesting is putting together these things which are kept separate. Advertising and documentary images are traditionally seen as different things but if you bring them together you can see the connnections."

In the 1980s Kennard worked with the Campaign for Nuclear Disarmament, the Greater London Council and the Workers' Press but the alternative publications he used to work for have largely disappeared, he says, and our public space is increasingly dominated by ads. He now shows his work via exhibitions, the internet and books, as well as in DIY public exhibitions in London's financial centre and on the separation wall in Bethlehem. @earth, his latest venture, is a small, hardback book published by Tate, which collects together work from his 40-plus year career. Divided into seven different chapters, it abandons written text in a bid to make it as widely understood as possible.

"The aim of it was not to do an art book," he says. "I wanted to make a book that could be understood globally, so the idea was to make the montage act as a language, and the book read as a narrative. It's a story without words." He deliberately kept the book the size of a small paperback to encourage people to 'read' it this way, and kept the price under £10 to try to make it attractive to youngsters and those outside the artworld. He also deliberately chose to make it a physical book rather than presenting the project online - a book priced £9.99 may be unaffordable for some, but at least costs nothing to read if you happen upon it, he argues. The internet can be more expensive and, for some, even harder to access.

The images are culled from all 40 years of Kennard's distinguished career because, the images from the 1970s are unfortunately just as relevant today as when they were made, he says. The book includes classic images such as his iconic world-in-a-gasmask montage, but it also references contemporary issues such as CCTV surveillance and The Bethlehem Wall via montages made with the artist Tarek Salhany The obvious criticism is that by combining such disparate issues, Kennard ends up making general platitudes such as 'war is bad' or 'pollution is bad', which fail to engage with the specifics of each situation that need to be negotiated in order to solve them. Kennard is aware of the problem, but says he's found no other way to handle it.

"In visual form you can't, or at least I haven't found a way to, make a specific argument in that way," he says. "But I've always tried to show individuals not big groups, to show individual human faces in different forms. I want to encourage people to think about their own situation and activate, but I'm not trying to tell them to do this or that. I'm just trying to show how I see the world at the moment."

@earth by Peter Kennard (assisted by Tarek Salhany) is published by Tate (ISBN 9 781854 379849), priced £9.99. The book can be bought at Tate publishing's online shop and in bookshops around the world.