When Jeremy Corbyn and Zarah Sultana announced a new political party this summer, it had all the ingredients to be a big success. But a summer of disarray has seen them overtaken by a rival on the left. What happened?

Three years ago travel writer Lydia Gard discovered freediving. An extreme and beautiful sport defined by one objective: to dive as deep as you can on one single breath. It soon became a calling. And then she stumbled on a darker side of the sport. Rumours were swirling that a group of top divers were doping to go deeper. So she decided to investigate. Deep Water is the latest Tortoise Investigates series from The Observer.

With Prince Harry in effective exile and Andrew disgraced, the Royal family is smaller than ever before and at a potential crisis point. Prince William has already signalled his intention to be a different kind of monarch to King Charles. But can the monarchy survive, and what is its purpose?