Engineers finished fitting 200t of steel superprops to the stricken elevated section near London yesterday afternoon after working flat out to get supports in place below the concrete bridge deck.

Both firms carried out the emergency propping work, along with structural experts from Atkins.

Supporting work was completed yesterday afternoon allowing part of the south bound carriageways to reopen around junction 2.

Engineers said it was a “miracle” the bridge had not collapsed because of the extent of fire damage.

They are now working to assess the full extent of damage to the main post-tensioned structural beams, where steel reinforcing rods have been exposed during the intense blaze.

Both the hard shoulder and lane one heading south are reported to be too dangerous to open, before extensive remedial works.

Roads minister Mike Penning, a former firefighter, said the intense heat from the fire had seriously damaged the concrete bridge making it “seriously unsafe”.

“It was so intense that some of the concrete has exploded and some of the steel has expanded which has made the concrete drop away,” he said.

“The inside lane on the hard shoulder was so badly damaged it is beyond repair and we’ll have to do remedial work on that later on.”

Structural engineers will now fully inspect the bridge.