It was one of the saddest events in Maidstone's history and led to a government department stepping in to make sure such a tragedy could never happen again.

On May 20, 1986, three young girls on their way home from All Saints Church of England Primary School (then in College Road) were killed when an articulated lorry ploughed into them as they walked along the pavement in Hayle Road.

Nine-year-old Sadie Wilkins, seven-year-old Lieanne Berry, and 10-year-old Marie Stone, were killed. Their friend Hannah Ingram, 11, was seriously injured – almost losing a leg and suffering a fractured skull. Marie's mum, Angela, who was walking with the girls was also injured.

One neighbour, who rushed from his home after hearing the crash, described seeing the children "lying like a row of fallen dominoes on the pavement."

Today, a plaque marks the spot of the tragedy.

It was immediately assumed by many that the lorry, a 32.5-tonne Mercedes Benz belonging to the haulage firm A Wood and Son (Detling), had been going too fast. It also knocked over a lamp-post, demolished a wall and smashed a road sign.

But a subsequent investigation found that was not the case.

The lorry's tractor unit had been fitted with exhaust brakes connected to the trailer brakes.

It had been raining and the driver Eric Nichol told an inquest afterwards how on approaching a bend in the road he had applied the exhaust brake to to slow the trailer. When the exhaust brake was applied, a valve was activated supplying air at a pre-set pressure via the service line to the trailer relay valve to apply the trailer brake.

He said: "As I applied the brake, I felt the back wheels juddering and bouncing as though the trailer brakes had locked on. I immediately came off the exhaust button."

He said he felt the back end of the trailer lift and assumed he had gone over some roadworks. He stopped the lorry and returned to the scene to find the dead and injured children lying on the pavement.

An expert from the Road Research Laboratory, Roy Rasdell, estimated the lorry's speed to have been 26mph, within the speed limit.

Detective Constable Barry Hill subsequently drove the lorry with its two-axle curtain-sided semi-trailer, away from the accident. He told the inquest he had applied the exhaust brake twice and found it "extremely excessive and potentially dangerous".

On the second occasion the wheels vibrated and the tandem axle see-sawed.

As a result of the accident, the Department of Transport issued a ban on all vehicles fitted with the exhaust brake system. The ban came into effect on September 30 that year.

Any vehicle found with that system at its MOT was issued with a GV9 notice, immediately prohibiting it from being driven any further on the road.

Kent Police vehicle examiner PC Ted Edwards told the inquest that in his opinion the accident had been caused by excessive air pressure to the trailer brakes during the course of using the exhaust brake.

But he stressed that the driver would have believed he was driving a very efficient system. He said: "Mr Nichol would feel the exhaust brake to be an additional safety measure, rather than a potential danger."

The inquest returned a verdict of accidental death on the three children.

A Wood and Son had 16 tractor units in its fleet fitted with the device, which it promptly removed.