A mum and her son were injured when an object, believed to be a ball bearing, smashed the windscreen of their car as they drove in Maidstone.

The terrifying incident in Salts Lane, off Loose Road, comes just days after an object was thrown through the windscreen of a gritting lorry while it was out treating roads in preparation for icy weather.

This afternoon police revealed there has been a third incident, when an object was thrown onto the M20 from a footbridge and hit a car.

The latest incident happened on Thursday underneath the footbridge for New Hythe Lane in Larkfield.

The windscreen was damaged and the driver reported seeing two people on the footbridge.

This happened the same day the woman's car was hit near Loose Road at about 6.50pm leaving her and her son with minor injuries.

The woman suffered a cut to her face and the ball bearing hit the boy's knee.

Police said they have sent the ball bearing away for forensic testing and conducted house to house inquiries in a bid to find the culprit.

The gritting lorry was working on behalf of Kent County Council when it was targeted on the A228 Snodland bypass beneath the Rocfort Road bridge about 6.45pm on Saturday, January 21.

Det Sgt Dan Barker said after the first incident: "Throwing objects at moving vehicles is incredibly dangerous and places people’s lives at risk.

"Fortunately the driver of the gritting lorry was not injured but we would like to hear from anyone who may have witnessed the incident or who has any other information."

Today police reminded people that anyone caught throwing objects at moving vehicles faces up to seven years in prison and fines of £1,000.

Their actions could also be fatal.

Inspector Rachel McNeil said: "Throwing anything at a moving vehicle is incredibly stupid and could easily kill someone, especially if they are travelling at high speeds on a major road.

"Fortunately reports of this nature are still rare, but those who commit such crimes could face serious repercussions."

In July 2010, a 47-year-old man died following a collision involving a lorry and a pick-up truck on the A20 Swanley interchange, after it was reported that stones had been thrown at the lorry.

Officers pledged to continue working with schools to educate pupils on the dangers of throwing objects at moving vehicles.

Anyone with information about the gritting lorry incident can call 01622 604100 quoting reference YY/1842/17 or email west.division.media.appeals@kent.pnn.police.uk. Call the same number with information on the Salts Lane incident and quote reference YY/2792/17. Alternatively contact Kent Crimestoppers anonymously on 0800 555111.