Our greatest landscape painter of the past century finally gets his just deserts from Tate Britain with this comprehensive exhibition. Most people know his astonishing world war paintings – The Menin Road from the first and Totes Meer from the second – but the show goes on to reveal how his horrifying experiences in the trenches on the Western Front in 1917 coloured his perception for the rest of his life and inspired some of the most memorable evocations of our countryside ever created. For example, the geometry of The Rye Marshes mirrors WW1 zigzag trenches while his painting of the sea-defences at Dymchurch makes them look like impregnable gun emplacements; yet in both cases the lonely beauty of the scenes remains absolute and unsullied. Less convincing are his experiments in surrealism.But don’t be put off by what is a mere quibble, for this is one of the best exhibitions currently running in London.