A TINY watercolour painting created just after the First World War is expected to fetch up to £40,000 at auction in Dorchester tomorrow.

‘Gas Alert’ was painted by sought-after war artist William Roberts and depicts five soldiers huddled together preparing for attack.

Amy Brenan of Duke’s, where the painting will go up for auction tomorrow, said : “This watercolour is a superb example of the work William Roberts produced during his time as an official war artist in the years 1918 to 1919.

"Influences of cubism- a style that he favored- such as the carefully angled hats and linear, sculptural faces, combine to give a bitter edge to the implied horrors of war that the subject matter represents.”

In 1916, Roberts served on the Western front as a gunner for the Royal Artillery and it is was his horrific experiences on the frontline that provided the impetus for his subsequent work.

He was later commissioned by the British Ministry of Information as official First World War artist in Canada.

The more paintings he produced, the more graphic they became and some of his most controversial First World War paintings can be found in the Imperial War Museum and the National Gallery of Canada.