One eye is shut in the agonies of approaching death. The other follows you around the room where Marc Chagall’s lost crucifixion has been exposed to public gaze.

In the last of ten attempts to depict the German persecution of Jews as a contemporary act of God-killing, Chagall in 1945 sketched a naked Christ-figure in a Jewish prayer-shawl and phylacteries, tormented on a cross by a creature with a Nazi armband, half-man, half-beast.

The sketch was found in a Paris auction catalogue by my friend David Glasser and bought for a paltry sum for the Ben Uri London Museum of Jewish Art. The discovery was reported last weekend in the New York Times and the work goes on display from today at the Osborne Samuel gallery in London’s West End in a limited showing of the Ben Uri’s extensive and largely unseen masterpieces by Jewish artists who lived in Britain.

The subject and date of the work endow it with a poignancy beyond words. The Christ figure has feminine hips, avoiding the sexual definition of so many crucifixion scenes to suggest the universality of a genocide that overrode compassions of gender. This Christ could be any Jew – man, woman or child – Chagall seems to be saying.

The martyr is surrounded by village scenes familiar from his Vitebsk period. But instead of fiddlers on the roof and cows that fly over the moon, the artist turns every sketch to horrors of hanging, inflagration, expulsion and death. It is a relentless lament for the world he left behind, a world that existed no more.

The eye of the martyr follows you around the room, challenging you at risk of your own humanity to turn your back on the calamity, forcing you to remember and engage. It is not by any means a finished work, nor possibly one of his greatest, but it registers ineluctably on first sight as one of his least forgettable. The exhibition runs to the end of the month.

More on the Ben Uri website: www.benuri.org.uk