The popularity of Impressionism has a lot to do with its escapist appeal: its philosophy of capturing the moment and distilling it into dappled colour and light. The political turmoil of the period presented French artists with plenty of reasons for escapism – and just as Impressionism was getting going, escape they did. The outbreak of the Franco-Prussian War in July 1870 caused a mass artistic exodus from Paris. Many artists fled across the Channel, followed by the art dealer Paul Durand-Ruel. The unlikely upshot, revealed in the National Gallery’s new exhibition, was that the commercial foundations of this most French of French art movements were laid in London rather than Paris.“Inventing Impressionism” (until 31 May) tells the heartwarming story of one man&rsq