A strike at the French port of Calais has led to travel chaos, with Eurostar services cancelled and part of the M20 motorway being closed.
Ferries are stuck at Dover and lorries have been parked on the M20 in Kent, waiting for services to resume.
The strike, which has now finished, led to suspension of services through the Channel Tunnel after protesters got on to the tracks.
Several Eurostar trains were forced to return to St Pancras.
There have been reports of travellers stuck at the London railway station and a heavy police presence.
A spokeswoman for David Cameron said he was being "kept updated" on the situation.
Workers from the MyFerryLink company went on strike and blockaded the port of Calais in a protest over job cuts earlier.
At 18:24 BST the company tweeted: "Industrial action in Calais now over and ships returning to service immediately. Our apologies to all affected by today's disruption."
In Kent, cross-Channel freight traffic waiting to cross from Dover has built up and Operation Stack has been implemented to close part of the M20 so lorries can queue there.
Despite the strike ending, Operation Stack will continue throughout the night and into Wednesday morning.
Dover Harbour Board said the industrial action closed the Port of Calais in the early hours and all ferries to and from Dover were affected, apart from DFDS Seaways services to Dunkirk.
Kent Police has said extra Dunkirk crossings had been arranged.
Lorry driver Chris Cary, from Rochester, said he tried to cross the Channel back to Kent early on Tuesday but decided to attempt getting on a train instead.
He said he found the road on fire as he approached the terminal with about 500-600 trucks waiting to cross.
Migrant activity is reported to have increased, with people attempting to board Kent-bound lorries in France.
The Foreign Office has warned travellers to keep their car doors locked in slow moving traffic heading back to the UK.
Tensions over illegal migrants at Calais have been rising, with the deputy mayor of the town blaming the British government for the number of people trying to board lorries.
Philippe Mignonet told BBC Radio Kent: "We will block the port - as simple as that. We'll arrange to block the tunnel if nothing is done".
Immigration minister James Brokenshire said the government had increased border security in both Calais and Dover.
"Border force are stepping up deployments in northern France and also at Dover as well with enhanced screening," he said.
"Ultimately it is for the French authorities to assure security and safety in France.
"We have been advised the French authorities are sending further policing to deal with law and order issues, and we will be keeping in close contact with them in the hours ahead."
- 23 June 2015
- 23 June 2015
- 28 May 2015