Mule Team, by the first World War artist CWV (Christopher) Nevinson – estimated at £250,000-£350,000 – is the top lot in the Modern British & Irish Art auction at Bonhams in London on Wednesday.

Mule Team was painted in late 1917 following Nevinson's return to London from a four-week tour of the trenches in his capacity as an official war artist and has been in private hands for nearly 100 years during which time it has been seen in public only once.

Against a leaden sky Matthew Bradbury of Bonhams said the "the subject of this picture – the stoical 'Tommy' plodding on with his mules against the leaden sky – is not noisily heroic, but more a reflection, after three years of war and no end in sight, of a quiet determination to see things through." He described Mule Team as "an exceptional work" and an "extremely rare" opportunity for collectors as most of Nevinson's wartime oil paintings are in museums.

Irish artists A selection of paintings by Irish artists in the auction includes The Bishop's Castle Tearooms by Sir John Lavery (£30,000-£50,000), depicting a scene at the 1888 International Exhibition of arts and manufacturing held in the park at Kelvingrove, Glasgow, is estimated at £30,000-£50,000; and, The Pool in the Bog, Achill Island by Paul Henry, £15,000-£20,000.