Nick Crane explores some of the most spectacular and scary sea cliffs in Britain. He embarks on an elevated journey to take in the high spots of the Yorkshire coastline. Tessa Dunlop meets a remarkable woman who witnessed a top-secret American 'invasion' of the English south coast during the Second World War. The US Rangers scaling the cliffs at Burton Bradstock were practising for their D-Day assault on similar terrain in Normandy. On the magnificent sea cliffs that surround Ramsey Island, biologist Sarah Beynon hunts for the superheroes of the insect world who do the island's dirty work, the dung beetles. They are critical to the success of the island's most famous wildlife residents, the choughs. Cassie Newland rummages through the extraordinary rubbish of ordinary people from the recent past at a cliff top dump at Lyme Regis which is sliding into the sea. Plus Andy Torbet takes part in a daring night-time exercise with commando recruits.

• Alice Roberts
• Miranda Krestovnikoff