Eurostar has cancelled 90 services, while major airlines are also warning of cancellations and delays.Read more
Essex Police have said investigators believe the lorry came from Bulgaria.
Speculating on the route the lorry may have taken, the chief executive of the British Road Haulage Association, Richard Burnett, said it could have travelled on a ferry from Cherbourg in northern France to Rosslare in the Republic of Ireland, before driving to Dublin to get a ferry to Wales.
He said it was "highly unlikely" the vehicle would have been physically checked if it had come from Europe.
"Because of the migrant issue at Dover and Calais, you've got far more checks that are taking place there," he said.
"You've got heartbeat monitors, you've got dogs, you've got CO2. Those checks are done as you drive through.
"Cherbourg, because it's a low-volume port, you probably won't have the same security measures that they have in Coquelles [Eurotunnel terminal] or Calais.
"If this is somebody trying to smuggle a significant number of people through then maybe Cherbourg has been picked because it's a little easier to get through."
To mark the Channel Tunnel's 25th anniversary the BBC was given exclusive access behind the scenes.
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