Any investigation into the M20 bridge collapse is expected to look into events leading up to the crash, plus how the bridge was maintained.

Pictures of the bridge from Google Streetview taken in October 2015 clearly show the joint where the bridge collapsed yesterday after being struck by a lorry on the London-bound carriageway.

The accident happened just after 12pm yesterday with repair work continuing into this evening, even as the motorway partially reopens.

People commenting on Kentonline say pedestrians still use the structure regularly and said it was fortunate no-one was on it when it came crashing down.

Questions are also being asked about what the lorry was doing apparently driving down the hard shoulder.

It is believed repair work was taking place to put higher barriers on both sides to help safety and stop people from throwing objects over the side onto the motorway.

Expert John Jermy, secretary of the Bridge Joint Association said it is not unusual to see such a collapse after a being struck by a vehicle.

He added: "Pedestrian footbridges are very slender and not designed to carry a load as heavy as those with roads running across them.

"It has taken a massive impact and the force of that would be enough to dislodge the middle section and bring it down.

"Quite often pedestrian bridges are put in place in three sections - two supports and a drop-in section in the middle, and it appears as if this middle section has come down."

He said his association was involved in a similar incident on the A2 near Dartford many years ago when a lorry hit a bridge and the road had to be closed.

"It is likely a division of the Highways authority will maintain the bridge and they are subject to regular checks. Various people will be contracted to maintain the motorway network," he added.

Officers from Kent Police’s serious collision investigation unit are now carrying out enquiries into the circumstances behind the incident, and are appealing for witnesses to get in touch.

The appeal line details are 01622 798538 quoting reference 27-0690 or email sciu.td@kent.pnn.police.uk.