The spirits of British poets and Romantic painters flit like moonbeams through fairy forests in this completely disarming exhibition. Paul Nash (1889-1946) painted the battlefields of both 20th-century world wars, and combined the ideas of the surrealist movement with a native feel for landscape. So much for the basic facts: Dulwich champions him with a passion that warms the heart.
The curator's clever choice is to show Nash's paintings outside chronology, which frees us from a prosaic trawl and enthusiastically draws attention to his strengths. Right from the start, you're in a distinctive, painted world that is part William Blake, part JRR Tolkien and all England. Red suns rise over chalk hills, grey breakers hit coastal defences. The landscapes of Kent keep recurring, along with unfamiliar views of London and, like a bass note building up to a sinister climax, the mudscapes of the first world war and the skeletal remains of Luftwaffe planes shot down in the Battle of Britain.
Surrealism was the one avant-garde movement of the early 20th century to which British artists took naturally. Its modern freedoms allowed Nash to paint his dreams, and mix up homely landscapes with personal myth in a way comparable to Dalì's mythologising of Catalonia.
Yet even when Nash takes surrealist photographs, his sensibility is as knotted as an English oak. Above all, his visions make you think of the nestled English village scenes painted by Blake's 19th-century disciple Samuel Palmer. It is a cliche that British Romantic art was always based on meticulous observation: it was pure inner revelation for Blake, for Palmer – and for Nash.
In the last room, the underlying note of war gets louder as you face Totes Meer (1940-41), a "dead sea" of German aircraft whose wings crash like metal waves on the English countryside. It is as if they have been absorbed into the timeless downland to become a new fairytale in this masterpiece, whose compassion for the enemy, given its date, is remarkable and inspiring.
Nash has always been an artist worthy of respect. Here he is rediscovered as one worthy of love.