Exploring the tidal ebb and flow of the seas surrounding Britain. Nicholas Crane braves the dangerous rapids off the coast of Anglesey, and investigates a tidal predictor in Liverpool. Miranda Krestovnikoff visits Jersey's Seymour Tower to witness the marine life revealed at low spring tide, Tessa Dunlop compares the fashions in bathing suits favoured by different generations of beach-goers and Mark Horton travels to Poppit Sands, Pembrokeshire, to explore the remains of a 900-year old fish trap.