The dun-coloured product, made from cork and linseed oil on a canvas backing, was cheap and about as workaday as you could get, which fitted Flight’s ideal of art for the “average man” rather than the privileged few. For “paint”, they used sticky, shiny printing ink, thinned with Vaseline. 

Flight recommended using old umbrella spokes and toothbrushes as tools. You can understand why some ­people thought it childish – even an art-world prank – but an exhibition of their work at the Redfern Gallery in Old Bond Street in 1929 sold 100 prints in its first days, with the V&A and the ­British Museum among the buyers.

Uglow conveys beautifully how lino’s pliable surface produced an exceptionally expressive stroke; one that implied the hurtle and whoosh, the heaving scramble and the sheer disorientating strangeness of the age like ­nothing else. In Power’s Whence & Whither? (1930), which pictures people on an underground escalator: “The hoops of the ceiling curve like giant teeth and the commuters’ dark bodies lean forward… The invisible city above is like a pressure on their heads.”

Both Power and Andrews produced several posters for London Underground, but their range extended far beyond it: umbrellas in a gale, ships on the sea, men ploughing, men mowing, rowing eights and much, much more. Indeed, The Eight by Power and Bringing in the Boat by Andrews, given to Uglow’s father by his best man (they had rowed in the college “eight” together), were the impetus for her book. Uglow has known them “all my life”, she says, though when it came to telling their stories, she had only the artists’ sketchbooks, appointment diaries and scrapbooks to work with; a “ragged collage” into which she has woven little darts of historical detail. You’re as likely to marvel at a tip from Good Housekeeping as a verse of TS Eliot.

Throughout, I was struck by the intensely visual prose, which makes the reader feel like they are flicking through a colourful sketchbook. Andrews first appears to us in a pair of black goggles, wielding an acetylene torch (she worked in an aircraft factory during the First World War): “The flashing sparks, the foot-long yellow flame flaring from the nozzle of the blowpipe, the smell of oil and hot metal, the shouts and quips and songs.” 

Elsewhere, snow covers London’s ruins “like a shroud, cloaking shattered walls and furniture”; Power’s high-Victorian childhood is one of “plush furniture, aspidistras and dinner gongs”, his children “trailing around in long Liberty fabric dresses”.

And even though the book is ostensibly about art, its characters come charmingly to life in their love of music. Power and Andrews were into madrigals and treble recorders, viola da gambas and German Dudelsack­pfeifer – enormous bagpipes. On their walls of their cottage in the New Forest, they chalked pictures of drummers and pipers, and St Edmund, for the Suffolk town in which they had met. Friends were invited over for medieval feasts at which they piped in the pudding.