The King and Queen have led the tributes to David Hockney - one of the most influential British artists of the past century - who's died at the age of 88. His large canvases, featuring boldly colourful landscapes and portraits, such as The Big Splash, hang in some of the most prestigious galleries in the world. In other news: SpaceX has officially started trading on the open stock market; and the prime minister has insisted that defence and security are his number one priorities for the country - despite the resignations yesterday of his defence secretary, John Healey, and armed forces minister, Al Carns, over the government's new defence investment plan.