Rohit Kachroo gains access to MI5, one of the world's oldest and most-renowned spy agencies. Filmed as London experienced two terror attacks at Fishmonger's Hall and Streatham, Tonight sees the engine room of the UK's fight against terror. Surveillance officers and investigators also discuss their secret work and its impact on their lives.

A healthy gut can do more than help digestion. It is being linked to everything from obesity levels to mental health. Five years ago actress Catherine Tyldesley made a film for Tonight about diets. Now she is back to find out exactly what people need to know about keeping the digestive system in good working order.