Helen Skelton, JB Gill and Jules Hudson explore the UK's coastline. In North Yorkshire, Helen descends 4,500 feet into the UK's deepest mine - the only place on Earth where polyhalite is extracted. On the Kent coast, JB explores Dungeness - a vast shingle headland and a haven for unlikely wildlife. Jules is in Devon, setting sail from Salcombe aboard the iconic Yawl - the pride of the south coast