BBC Four Today

Barra Best sets out to uncover and explore some of Northern Ireland's lost railways, beginning with a visit to Co Down's answer to Stonehenge and a trip to the races

The naturalist reveals exactly how an asteroid strike wiped out the dinosaurs after an enormous asteroid hit Earth some 66 million years ago

Kirsty Young talks to David Attenborough about his life and career. Featuring footage from his many natural history programmes and contributions from colleagues and friends

Peter Egan looks back on the 1987 adaptation of John Le Carre's A Perfect Spy, reflecting on the making of the series and the challenges that came with adapting Le Carre's work

Seven-part detective series adapted from the John le Carre novel of the same name, starring Ray McAnally and Peter Egan

Magnus is sent on an errand to Switzerland, where he meets someone who will become important in his life as a spy

Magnus betrays his father and renews his acquaintance with Axel. Detective series adapted from the John Le Carre novel of the same name, starring Ray McAnally and Peter Egan

Kirsty Young talks to David Attenborough about his life and career. Featuring footage from his many natural history programmes and contributions from colleagues and friends

The naturalist reveals exactly how an asteroid strike wiped out the dinosaurs after an enormous asteroid hit Earth some 66 million years ago