Two off-duty emergency service workers were sprayed in the face with an unknown substance in what police have called a "shocking incident".

A police officer and paramedic were among Good Samaritans who stopped to help a car that had collided with a lorry on the M11 on Friday at around 7pm and was on fire.

Essex Police said as those inside the stolen blue VW Golf got out of the vehicle, they sprayed an unknown substance into the faces of the two off-duty emergency responders.

Chief Superintendent Luke Collison said: "This was an shocking incident and we have launched a significant investigation to track down the suspects and bring them to justice.

"Good Samaritans who witnessed a serious collision stopped to provide urgent medical care and were met by two dangerous offenders and seriously assaulted."