I am the first to admit that King Lear, of Shakespeare’s great tragedies, is the one that fills me with little joy at the prospect of seeing it again. But here at London’s Donmar Warehouse with Michael Grandage at the helm and Derek Jacobi in the title role is a production to prove my misgivings not just unfounded but as foolish as the old man. This is the definitive Lear for my money, the one to which all others should aspire. Nothing annoys. Nothing grates. All builds a perfect and avoidable tragedy.