He was already acknowledged as a key figure of painterly expressionism, seen at its best here in later works such as London, Tower Bridge, where the handling takes flight in what might otherwise have been a picturesque cliché.

Both artists represented familiar subjects such as actors and circus performers - the sort of thing Sickert liked. But there's a political element too in the choice of work on show. Kokoschka's bitterness against Fascism is clearly stated in a powerful painting from 1940, The Red Egg. Friends and family are also represented in works that convey a strong sense of nostalgia.

Yeats's treatment of the circus as subject-matter is heavier than Kokoschka's. There's an element of brutalism in his early images of performers that at times seems almost Goyaesque. But he tears all this apart in the later work.

The fractured surfaces of two stunning little paintings, The Singing Clown and They Love Me, open up a territory of expressionism that Kokoschka would never as comfortably inhabit.

You can see why they influenced each-other, but Kokoschka's scope and his breadth of experience always comes sailing through.

With both artists, though, their 'handwriting' is much in evidence. Their warts and all frankness is a hundred miles from Michelangelo's man as the measure of all things. It's quite simply a more modern approach. Peter McCarthy