Fire investigators believe a scrapyard blaze that caused massive disruption to travellers on the M1 was started deliberately.
The fire under an elevated section of the motorway in Mill Hill, north London, led to huge delays for football fans and marathon runners travelling to and from the capital at the weekend.
Experts have now concluded that the blaze was the result of arson.
A London Fire Brigade spokeswoman said: "We believe that the fire was started deliberately and the incident has now been handed over to the Metropolitan Police for investigation."
Two lanes were open in each direction along the affected seven-mile stretch of the M1 between junctions 1 and 4 on Tuesday.