Rex Harris, Church in the Downs, pre 1939. ©The Artist's Estate. Salford Museum & Art Gallery

Look at this: a painting of a worker, crucified. Here is an image of poverty that shocks despite the obviousness of the metaphor. At the foot of the cross sits his grieving wife and dog. On his left some co-workers shake their fists at three Bullingdon Club types on the right. A soldier armed with a rifle protects the nabobs. In the background policemen on horses bop strikers. Is this a vision of now? Is it by Coldwar Steve? No – this is An Allegory of Social Strife, the work of Archibald Ziegler done sometime in the 1920s. Ziegler? Who he? Who knew we had our own George Grosz?

You could ask that question – who knew? – about many of the artists here. The Towner knows them and they’ve curated a fascinating display that seems determined to resurrect reputations in much the same manner as the museum contributed to the popularisation of the long-ignored Eric Ravilious.

The connection between this terrific pair of shows is the remarkable Lucy Wertheim. Wertheim, a gallerist and early supporter of Barbara Hepworth and Victor Pasmore (both have important early works here), was the inspiration behind the Twenties Group, a collection of British artists under thirty, often referred to at the time as a ‘nursery’. Frustrated by the lack of attention these artists had in comparison with their continental peers, Wertheim championed their cause with highly focused intent.

Many of these artists were not from the privileged classes. As the informative wall texts here tell us she was “drawn to the under-represented, whether this was based on youth, old age, sexuality or gender”. She had great sympathy for artists “struggling to make ends meet”, whose poverty, as with Frances Hodgkins sat in a basement flat without water or light. Wertheim was determined they “should achieve fame!” and that “the public should be educated to an appreciation of these ‘Masters of Tomorrow’”. Oh, for more people like Wertheim around in the art world of Britain today…

The artist she perhaps championed most was the tragic figure of Christopher Wood. Wood’s maritime imagery is substantially represented here as with French Crab Boat, Tréboul, France (1929). These canvases have a near briny reek about them, a marine saltiness; you sense the woozy quop of the waves. Wood was dead at twenty-nine, a doomed Chatterton of the canvas. His life is outlined in Sebastian Faulks’ excellent The Fatal Englishman (1996). Wood was an epigone of Picasso, a mate of Cocteau, and fellow opium enthusiast. According to a newsboy at Salisbury railway station Wood “sort of ran and jumped and dived and screamed” in front of an oncoming steam engine. His Little House by Night (1930), painted in the year of his death, has hints of his imminent departure, an enigmatic black figure with its back to us enters a cottage – a table outside has a bottle of wine and a couple of playing cards that suggest the inexpressible. There’s an Ace of Hearts, a goodbye to love and life perhaps?

Installation shot: Rob Harris

What was it with the Twenties Group and water? Fluvial and seascapes feature strongly as with Suzanne Cooper’s Thames in October (1936), a brilliantly busy composition reminding us how industrious the river once was. A couple of steamers sail in opposite directions. A rail bridge spans the flow, the painting elaborated further with signals and falling leaves and gulls. Partners Kenneth Hall and Basil Rákóczi painted on the Aran Islands, luxuriating in the coastal vistas and the sight of currachs bobbing on the swell. Rákóczi’s Sleeping Islander (1943) is a lazy vision of Celtic indolence straight out of Flann O’Brien.

There’s more surrealism with Dieppe (1931) by John Selby-Bigge, a de Chirico-like composition with the horizon painted at different levels, the boats unmanned, a piece of wall in the foreground broken up into Lego pieces. Staying by the sea there’s a surprise: Sarkese Fisherman (1933) is by Mervyn Peake of Gormenghast fame. The rough rendering of the man’s massive, gnarled, arthritic hands suggest that Peake was much influenced by Van Gogh.

Wertheim supported artists from all walks of life. She was a fan of Henry Stockley, a bus driver, who painted his primitive colourist takes about London life onto strips of lilo. George Bissill was a miner and his woodcut here, Untitled (preparing to blast a coal face) (post 1925), has all the grim muscularity of a Peter Howson. The communist Clifford Hooper Rowe lived a year in the Soviet Union of the 1930s. Once home, his social realism-inspired The Fried Fish Shop (1936) is a very British vision of proletarian pleasures, a sign behind the workers says proudly “Harry’s for Quality”. Elsewhere Sylvia Melland’s Outpatients, Manchester Royal Infirmary (1934–7) has the melancholic dignity of a Lowry with its patient patients, its bright white-clad midwife handing over a baby in the gloom of the big brown room.

There are images of opulence on display too as with the vermillion flowers in front of Window at No.5 Portland Place (1938) by Rowland Suddaby, a man described as arriving in London with “no prospects or connections”. In another part of London, Suzanne Cooper’s Bloomfield Terrace (1936) is a jolly street scene with a Tati-like air; it’s a place you’d want to live in.

Robert Greenham, On the Beach, 1934. ©The Artist's Estate. Image courtesy The Ingram Collection

The fascination with water and motion displayed here reflects the geopolitical flux of the interwar years, a sense of uncertainty. There’s a hint of Orwell’s mood in Coming Up for Air: a fragile world where modest, transient, pleasures – fish and chips, a trip to the seaside – have to be seized before the hammer falls. This is typified by On the Beach (1934), a work by Robert Greenham, with its glam pink and lilac shadows, a glimpse of pleasure before the rain.

There’s a tragic undertow to many of the stories here with tales of suicide (Hall, Wood, Vivian Forbes), early post-operative death (George Branson), and general neglect. We are told that, postwar, woman artists in particular had to “put aside their aspirations to be artists to dedicate themselves to their families or another career path.” And then there’s Rex Harris, a painter “fallen into complete obscurity”. His Sussex Landscape (pre-1937) is the work I’d take home – an exquisite watercolour of the Downs with purple rainclouds above the smooth green hills and a lone speckled stone church.

“Why can’t they see?” This is Wertheim crying out in Adventure in Art, her memoir from 1947. She is scathing about the visitors to her gallery, reduced to “a state of exacerbation by their utter lack of comprehension”. She had a beady eye on the bourgeoisie: “I now see that the crowds who visited my gallery … did so not so much for love of art but because it was the thing to do.’ Not now. Nearly a hundred years later the crowds here are agog at her taste and foresight. Despite the sadness of long-standing oversight, this is a joyous show.

A Life in Art: Lucy Wertheim, Patron, Collector, Gallerist/Reuniting the Twenties Group: From Barbara Hepworth to Victor Pasmore is on at the Towner Gallery, Eastbourne, until 25 September