The fourth programme in an eight-part series in which Professor Aubrey Manning seeks to solve some of the enduring mysteries of the British landscape through clues in geology, archaeology and natural history. In this programme, Professor Aubrey Manning collects evidence of a flooded landscape beneath the Solent. The explanation is the land movements that have occurred since the melting of the huge layers of ice that were centred on Scotland more than 8000 years ago. As the weight of ice over Scotland was reduced, the land rose. The UK effectively tilted and southern Britain sank slowly into the sea. The effect is still going on and Antony Long from the Environment Research Centre is one of those involved in vital work to gauge the advancing sea levels and decide on the best response. As the sea encroaches further into low lying areas of southern Britain, the main question is whether to build ever bigger barriers or simply to allow the advance to progress naturally, with the accompanying salt marsh forming its own barrier.