Labour is calling on David Cameron to demand compensation from France for hauliers, businesses and holidaymakers affected by chaos at the port of Calais.
In a letter to the Prime Minister, acting party leader Harriet Harman said Mr Cameron's reaction to the crisis had been "devoid of any serious solution", and accused him of inflaming the problem with "incendiary and divisive language".
The call came as the M20 motorway was reopened for normal traffic after the last lorries being held under Operation Stack procedures were allowed through to the Channel Tunnel and ferry ports.
Announcing the lifting of Operation Stack, which has seen thousands of lorries parked on the coastbound carriageway for much of the past month, Kent Police warned that residual delays could be expected in the area.
Mr Cameron phoned French president Francois Hollande on Friday to discuss their response to scenes of migrants besieging the Channel Tunnel entrance at Calais, which the PM warned he expects to last all summer.
Measures promised by Mr Cameron, including more sniffer dogs and fences, were dismissed by hauliers' representatives as "a sticking plaster".
French police told the BBC that fewer migrants attempted to enter the Eurotunnel terminal in Calais overnight than in previous days, with around 800 gathering by security fencing and 300 making it into the secure area.
Ms Harman said the PM had ignored repeated warnings about the crisis developing in the French town, where as many as 5,000 migrants are living in a makeshift tent city awaiting their chance to cross the Channel to the UK.
She quoted Freight Transport Association estimates that the crisis is costing hauliers £700,000 a day, while there are further costs for Kent businesses and residents and families trying to travel to the continent.
Conservative MP Helen Whately said the motorway shutdown was a "nightmare" for people in her Faversham and Mid-Kent constituency, though she was "optimistic" of improvements after Mr Cameron got personally involved.
Ms Harman told the PM: "It is wrong for UK businesses and families to face these costs given border security failures in France. Your discussions with the French government should therefore include a request for compensation backed up by any diplomatic pressure that may become necessary. Compensation should cover all losses.
"Over the last few days, your approach has been devoid of any serious solution to the crisis. You have failed to initiate any diplomatic pressure on the French government to assess asylum claims and make sure proper immigration procedures are followed. Instead you have chosen to inflame the situation with incendiary and divisive language, which will serve only to escalate the problem."
Labour pointed out that the French authorities had paid compensation to UK hauliers in previous incidents causing them serious disruption, such as industrial action by lorry drivers in 1996.
After chairing a meeting of the Government's emergency Cobra committee in Whitehall on Friday, Mr Cameron branded scenes of migrants breaking through fences and hanging onto lorries as they try to enter the Channel Tunnel "unacceptable" and declared: "We are absolutely on it. We know it needs more work."
Options to relieve traffic back-ups on the M20 under consideration included the use of spare car parking space at Ebbsfleet railway station or the disused Marston airport, as well as increasing capacity on other ferry routes.
Laws including new powers to tackle illegal working will be fast-tracked, while Britain and France plan to put on flights to return migrants to their home countries.
Downing Street said that both the Prime Minister and Mr Hollande expressed concern about the "immediate security challenges" at Calais and reiterated their commitment to "continue working closely together to tackle the problems posed by illegal migration".