A teenager is being held under the mental health act after broadcaster Sir Trevor McDonald's wife spotted him acting suspiciously near the couple’s East Sheen home.

The 19-year-old was taken to an undisclosed secure unit after Mrs McDonald, and other neighbours, saw him hanging around the house at about 3.20pm on Monday.

One eyewitness told how the teenager lay on top of a full-looking white bag when police arrived to take him away. After a brief struggle three police officers took the young man to hospital. No injuries were reported and police are still investigating the incident.