Labour’s acting leader has written to David Cameron calling for compensation from the French government for UK people affected by the Calais crisis.
Harriet Harman said people and businesses should not bear the cost for “border security failures”.
But Downing Street said pointing the finger of blame was not the right way to find a solution.
Calais migrants are making nightly bids to cross the Channel. The UK and France have pledged to tackle the issue.
Mr Cameron has already offered extra sniffer dogs and fencing for Calais.
Eurotunnel and ferry services were running to schedule on Saturday evening after delays earlier.
Operation Stack, under which lorries queue on the M20 in Kent owing to cross-Channel delays, had been stood down, Kent Police said, and the motorway is open in both directions.
In her letter, Ms Harman said the UK government had “ignored repeated warnings” about the worsening situation at Calais.
She said it was “wrong” for UK businesses and families to pay costs resulting from the ongoing problems.
And she called on Mr Cameron to request compensation from the French government “backed up by any diplomatic pressure that may become necessary”, saying it should cover all losses.
Ms Harman also criticised Mr Cameron for his use of the word “swarm” when describing migrants trying to reach the UK.
“Over the last few days, your approach has been devoid of any serious solution to the crisis,” she wrote.
“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.”
Ms Harman said she hoped Mr Cameron would make an “urgent diplomatic effort” with France and other European countries and asked him to say how he planned to deal with people trafficking and the “refugee crisis” in the long term.
Scotland’s first minister has also written to Mr Cameron to express concern over the impact of the Calais crisis and its humanitarian issues.
In her second letter to the prime minister on the matter, Nicola Sturgeon said the UK must ensure it took part in the EU’s proposed relocation scheme and look at short and longer-term solutions.
Ms Sturgeon reiterated her concerns about the impact the situation had had on business, in particular seafood exports from Scotland.
A Downing Street spokesman said the prime minister was keen to have a constructive relationship with the French.
The spokesman said the government “sympathises” with hauliers and businesses and that he was “doing everything possible to get things moving again”.
Mr Cameron spoke with French President Francois Hollande on Friday night about the situation in Calais and the two governments were working “hand-in-glove”, he added.
The UK is offering to replace green mesh fencing at the Eurotunnel entrance perimeter in Coquelles with solid fencing of the type normally seen at Nato summits, in addition to more Border Force search and dog teams.
Calais migrant crisis
Impact on Kent council social services
the number of unaccompanied children seeking asylum that require care from Kent county council
220 the equivalent number in March 2014
£5.5m funding shortfall according to the council
French Police said about 800 migrants had gathered near security fencing at Calais on Friday night, and about 300 had made it into “secure” areas.
Officers said it had been a quieter night than others recently, but they acknowledged dozens of migrants may have made it on to lorries and into freight carriages in trains.
There have been thousands of attempts by migrants to access the Eurotunnel terminal this week.
A man believed to be Sudanese was killed on Tuesday night while attempting to make the journey. He is the ninth person to have been killed trying to access the the tunnel since the start of June.
Migrants told BBC new correspondent Gavin Lee they were exhausted after days of attempts to access the Eurotunnel terminal.
More than 600 French riot police are in Calais, working with local police.
Jerome Vignon, who has been working on a report about migrants in France, said they were unlikely to be deterred by extra security measures.
He said many migrants had travelled for 18 months to reach Calais, by which time they had “suffered a lot and they are out of cash” and were determined to reach the UK.
“So increasing security will be increasing casualties, I’m afraid,” he said.
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