A lorry driver had a lucky escape when a rock was thrown from a bridge over the M25 and smashed the windscreen of his cab.

Police are now appealing for wtnesses who may have seen three children at the footbridge - locally known as the Ovaltine bridge - between junctions 20 and 21 at 3.15pm on Saturday.

The children waved as the lorry approached but when it got closer one of them dropped a rock which hit and smashed the windscreen. The driver escaped injury.

The three children were described as being white and aged between 11 and 12. Two of them were wearing grey tracksuits, the other was wearing a dark blue tracksuit.

PC Owen Nee from the Bedfordshire and Hertfordshire Roads Policing Unit is investigating and said: “Incidents such as these can have extremely serious consequences but thankfully in this case the lorry driver was not injured.

“I would like to speak with the children who were on the bridge. We believe two of the children in the group were not directly involved in what happened. If anyone knows who they are or who saw what happened I would ask that you contact police.”

Anyone with information is asked to contact PC Nee via the Herts Police non-emergency number 101.