Under grey skies in London yesterday, David Hockney arrived at Tate Britain to see the gallery put on display his biggest work, Bigger Trees Near Warter (2007). The oil painting of a grey day in east Yorkshire, valued by the Tate at £10m, is undeniably huge, 15ft by 40ft. The artist said, "Once you live in a place like California, well, you need the rain. I used to think there were dull days and now I think it's only you … dull people."