A cooking oil spill continued to cause havoc on the M25 on Wednesday, 24 hours after a road traffic collision involving an HGV.
Drivers complained about queues on social media as specialist teams set about the clean-up operation.
The M25 was closed from junction 23 to junction 25 near Hatfield to clear the oil after the collision, which occurred at 11.16am on Tuesday and saw large amounts of cooking oil spilled over the eastbound carriageway.
Miles of stationary traffic was captured on camera by commuters on Tuesday on what was the first day back at work for many after the Easter bank holiday.
A National Highways spokesman said on Wednesday morning that lanes three and four had reopened to traffic, but lanes one and two were yet to be cleared.
"I can confirm that two lanes have reopened on the clockwise M25 near Hatfield after a protracted clean-up operation of vegetable oil as a result of a collision yesterday," said Duncan Smith, National Highways executive director of operations.
"Vegetable oil is a very difficult substance to remove from the road surface.
"Anyone who has spilled it onto work surfaces or clothing at home will know just how problematic it can be, so clearing gallons of the substance from one of the busiest roads in the country is no easy task.
"We have had specialist teams working on the M25 overnight and they are continuing the clean-up operation to try and get the road fully open as soon as possible."
Mr Smith offered his apologies to those affected by the delays, and thanked drivers "for bearing with us" during the clean-up operation.
A tweet from @HighwaysEAST on Wednesday morning said that the cleaning work was "likely to be ongoing throughout the day and overnight".