Born in Australia, Dyson revolutionised British cartooning during the three decades leading up to the last war by restoring the radical and irreverent tone that had been smothered by stuffy Victorian correctness.
It was only last year, while researching Dyson's career on such titles as The World and the left-leaning London Daily Herald, that John Jensen, himself a well-known cartoonist, heard about a chest stored away in the attic of the Kensington home of Baroness Yves Chanteau, the British-born widow of a French aristocrat. The chest, which had lain forgotten for 40 years, was believed to contain a handful of Dyson's works.
Jensen, who was already keen to stage a Dyson exhibition drawing upon existing private collections, rang the Baroness to check if she had anything worth including: the trunk had apparently been bequeathed to her by her husband's first wife - Dyson's only daughter, Betty.
When the big red box was finally lumbered down into the Baroness's study, unpacked and its contents spread out across the room, it turned out to contain hundreds of Dyson originals - cartoons and drawings in pencil, charcoal and crayon, as well as etchings and engravings. Jensen, who chairs the British Cartoonists Association, found himself leafing through scores of startling black-and-white images of British and American society, many up to 85 years old and never previously known to exist.
The Chanteau Collection, as it is now called, contains the best of the high-water period of Dyson's career - between 1912 and 1919 - when he made himself equally unpopular with Left and Right by ripping into both the Establishment and the Labour Party and trade unions. As a war artist, Dyson also created some of the most haunting images of the Western Front, drawings that made him a huge celebrity in Europe and the USA.
No collection in either Britain or Australia can boast anything like the breadth and quality of the work that was scattered around the Baroness's study that day.
"I was standing there, looking round at it all and I couldn't believe it," Jensen recalls. "I think I used a term my father used to use ... 'Oh, Jesus!' It's a huge number of drawings. I couldn't really come to terms with it. Here were drawings which I'd always assumed had been thrown away. Some I had never seen before or didn't even know about. There were drawings Dyson had obviously looked at and thought were no good and decided to chuck away but then put to one side because they might have contained little pieces of craftsmanship he valued."
Jensen called in Robert Edwards, the director of Kent University's Centre for the Study of Cartoons and Caricature, who was also stunned by the collection.
"It's tremendous, a very rich find," Edwards agrees. "The drawings are in various degrees of ageing. It's almost like an archaeological find, in the sense that there's dust and some of the drawings are torn, but overall most of them are in remarkably good shape."
Over the past 25 years, as part of its archive of around 85,000 drawings, the Kent Centre has gradually accumulated several hundred Dyson works from various sources. "But the Chanteau find dwarfs a lot of the material we have at the university," Edwards says. "To find a large intact collection like this, cartoons of this age, at the turn of the century, is very rare."
Dyson's great achievement, the experts say, was reimposing on the craft of satirical cartooning the cutting edge of James Gillray, the great 18th- century engraver and caricaturist who turned his ferocious ridicule on every possible target - William Pitt, George III, the Tories, the Whigs, the French Revolution and later Napoleon.
"Before Dyson, things were pretty tame," says Edwards. "Punch, Vanity Fair and people like Max Beerbohm had certainly caricatured public figures, but they had used kid gloves. Dyson brought back the tradition of Georgian satire. He was the first one to make it a savage satirical scene in London again."
During his own career since 1950, drawing for publications as diverse as Punch, New Statesman and the Evening News, Jensen has grown concerned that the place of Dyson as the forerunner of the greatest cartoonist of them all, Sir David Low, has never been fully appreciated. He and Edwards are still flabbergasted by what the Chateau Collection reveals of Dyson's technical range.
Jensen and Edwards have been lobbying to get a national museum of cartooning established because of their concern that computer image-making is slowly killing the art form. For the moment, though, they are content to be getting the Dyson exhibition staged at last.
More than 100 of the best Dyson works, drawn from the Chanteau and other private collections, are to be unveiled at Australia House in London this Tuesday. The exhibition includes one of the great gems of Dyson's career - his legendary 1913 drawing of the Labour Party abasing itself before world capitalism, as symbolised by a huge, light-radiating top hat. The caption reads: "Labour leaders at their devotions."
The owner of the 1913 drawing, the son of a former London Herald editor who received it as a gift from Dyson himself, wrote to Tony Blair recently, offering it for his office wall. A letter from one of Mr Blair's researchers came back, politely refusing the offer.
n Will Dyson's work is on show at the Exhibition Hall, Australia House, London WC2 from Tuesday until 4 Oct, 9.30am-3.30pm. Admission is free. For further details call 0171-887 5223