In this episode, the team look at Britain under pressure. With the population of the UK topping 63 million, what are scientists and engineers doing to reduce the strain on our ageing infrastructure? Maggie heads 50 metres beneath the River Thames to see how the UK's biggest ever water engineering project aims to prevent raw sewage flowing into the Thames every time heavy rain overwhelms London's sewers; Liz explores the possibilities of urban underground farming, and also finds out how engineers protect us from smells like landfill; while Jem investigates a new idea that could help to tackle the problem of overcrowded graveyards.

• Dallas Campbell
• Liz Bonnin