Trains were confined to their sidings when the Channel Tunnel was closed after a fire broke out on a freight service on Thursday.
All services were cancelled after the blaze started on a France-bound lorry about seven miles from the tunnel exit.
The disruption caused frustration for weary passengers who were stranded at St Pancras International station in London.
On the other side of the Channel, Eurostar passengers unable to complete their journey had to return to Paris's Gare du Nord terminus.
Some 300 firefighters - 100 of them British - tackled the fire which involved a vehicle carrying the chemical phenol.
At the French entrance to the tunnel the military stood guard as the marathon firefighting operation continued.
Kent Police introduced Operation Stack as freight vehicles were parked on the coastbound carriageway of the M20 though the night.
There was little change the following morning. French police later said the fire had been put out after more than 16 hours.