Prince William was one of the air ambulance crew members called to St Albans yesterday after an ambulance and car collided.

The helicopter pilot joined the East Anglian Air Ambulance as they responded to the incident on Watford Road at around 10am.

One person is in a critical condition and three others were injured in the collision involving a car and an ambulance responding to an emergency call.

No patient was on board at the time but two ambulance staff and two members of the public were taken to hospital.

Students from West Herts College were on a field trip with lecturer Jirapa Harding when they spotted the future King in Cassiobury Park.

Mr Harding said: "The students were very impressed, but weren't allowed any selfies."

A man, thought to be in his 50s, was flown to the Royal London Hospital with critical injuries.

An elderly female sustained a serious head injury and suspected fracture and was taken to Watford Hospital by land ambulance.

Two ambulance service staff were also taken to Watford Hospital. One sustained a chest injury and the other was said to have minor injuries.

The ambulance was on its way to a 999 call-out. The patient was treated by other paramedics.