Huge queues of lorries on both sides of the English Channel begun to move after just over half the usual number of ferries started sailing between Dover and Calais.

Calais had been closed to most ferry traffic for four days because of a strike by French ferry workers – a situation that prompted the Government to hold an emergency Cobra meeting, putting a labour dispute on a par with terrorist attacks and foot-and-mouth disease as threats to the nation.

Tim Waggott, chief executive of the Port of Dover, warned that the disruption to services was costing the UK economy at least £250m a day.

However, following a meeting between French government ministers and union officials, there was a breakthrough that enabled Calais to open two berths for P&O vessels despite the industrial action by MyFerryLink staff over expected job cuts.

Lorries parked along the M20 at Ashford, Kent (Getty)

Queues of up to 7,000 lorries have built up in Kent, but P&O said it should be able to clear the backlog within two days. The Port of Dover said there were still no sailings to Calais by MyFerryLink and DFDS Seaways, the other main ferry operator. DFDS was however running services to Dunkirk.

The Cobra meeting was chaired by Oliver Letwin, the Minister for Government Policy. The Home Secretary, Theresa May, was in Paris to meet her French counterpart, Bernard Cazeneuve.

In pictures: Calais crisis Show all 15 1 /15 In pictures: Calais crisis In pictures: Calais crisis Calais crisis Migrants climb in the back of a lorry on the A16 highway leading to the Eurotunnel in Calais Getty Images In pictures: Calais crisis Calais crisis Protesting French employees of the company English Channel passenger and freight ferry company "MyFerryLink" block the railway tracks of the Eurostar Channel tunnel line in Calais Getty Images In pictures: Calais crisis Calais crisis Protesting French employees of the company English Channel passenger and freight ferry company "MyFerryLink" block the railway tracks of the Eurostar Channel tunnel line with a burning plastic barrier In pictures: Calais crisis Calais crisis French riot police officers drive out protesting French employees of the freight ferry company MyFerryLink Getty Images In pictures: Calais crisis Calais crisis French riot police take position to drive out protesters blocking the railway tracks Getty Images In pictures: Calais crisis Calais crisis Passengers stranded by the cancellation of Eurostar trains wait at St. Pancras station in London. Eurostar said it has canceled all passenger trains through the tunnel that links France and England, after striking ferry workers swarmed the train line setting tires alight In pictures: Calais crisis Calais crisis Passengers sit on stairs after being stranded by cancelled Eurostar trains at St. Pancras station in London In pictures: Calais crisis Calais crisis A police vehicle drives past lorries are backed up on the M20 motorway which leads from London to the Channel Tunnel terminal at Ashford and the Ferry Terminal at Dover In pictures: Calais crisis Calais crisis Trucks queue up as part of Operation Stack in Dover In pictures: Calais crisis Calais crisis Cars queue to board a ferry in Dover bound for Dunkirk, France, as the disruption at Calais looks set to enter a second day as migrants continue to target lorries in a bid to cross into the UK In pictures: Calais crisis Calais crisis A police officer sprays tear gas to migrants trying to access the Channel Tunnel on the A16 highway in Calais, northern France PHILIPPE HUGUEN/AFP/Getty Images In pictures: Calais crisis Calais crisis Migrants wait near the A16 highway as they try to access the Channel Tunnel in Calais, northern France PHILIPPE HUGUEN/AFP/Getty Images In pictures: Calais crisis Calais crisis Striking employees of the French company My Ferry Link, a cross-channel ferry service, stand in front of tyres set on fire as they block the access to the Channel Tunnel in Calais, northern France PHILIPPE HUGUEN/AFP/Getty Images In pictures: Calais crisis Calais crisis A striking employee of the French company My Ferry Link, a cross-channel ferry service, sits on a tyre in front of tyres set on fire as he takes part in a blockade of the access to the Channel Tunnel in Calais, northern France PHILIPPE HUGUEN/AFP/Getty Images In pictures: Calais crisis Calais crisis Striking employees of the French company My Ferry Link, a cross-channel ferry service, prepare to set tyres on fire to block the access to the Channel Tunnel in Calais, northern France PHILIPPE HUGUEN/AFP/Getty Images

Ms May and Mr Cazeneuve issued a joint statement which said they had “emphasised the importance of a rapid resumption of maritime and rail traffic, which is indispensable to economic development on both sides of the Channel”.

The main point of the meeting was to discuss thousands of migrants who have been attempting to cross the Channel by hiding on lorries and other vehicles, a problem made worse by the traffic jam on the French side.

Ms May agreed that the UK would pay more money into a £10.6m fund designed to increase security at the Port of Calais.

“This will enable the installation of additional essential arrangements to prevent access to the port via the beach, but also to secure access to the Channel Tunnel, where incidents have taken place repeatedly over the past weeks,” they said.

A campaign “to inform migrants of the reality of Great Britain’s asylum and benefits system, to reduce the flow of migrants to Calais” will also be stepped up.

Dan Bridget, a spokesman for P&O Ferries, said its services would be operating normally on Friday with 25 round trips a day between Dover and Calais. “We’re delighted to be back to business as usual,” he said. “I think the numbers of lorries waiting in [Kent] has been oscillating between 3,000 and 7,000. In the worst-case scenario, it will take us two days to move that freight.”