As his Velvet Revolution drama returns, the great writer talks about his mounting Israel-Gaza uncertainties, the epiphanies he has in every hot shower " and our one-star 'corker' review of The Crown Tom Stoppard is chatting in the theatre bar when I arrive to interview him about a revival of his play Rock 'n' Roll. He was comparing ailments with an elderly director friend, he says cheerfully, as he heads up the stair…