British officials were drafted in to help French border police yesterday after 15-hour queues built up at the port of Dover due to heightened entry checks.
Stationary vehicles could be seen snaking through the countryside, inland from Dover at England’s southeastern tip.
The town is Britain’s main ferry port to Calais in northeastern France, 33kms across the Channel.
Under a reciprocal agreement, Britain and France have border controls on the opposite side of the Channel.
“We recognise the security pressures that French law enforcement organisations are under at Dover and we have agreed the UK Border Force will assist the PAF (French frontier police) with border checks to remove the backlog,” said a spokeswoman for the Home Office.
“There has been extraordinary disruption in the Dover area but safety is paramount.” 
Some people slept overnight in their cars.
Highways England, which runs the road network, told drivers: “French border police at the port of Dover and Eurotunnel continue to follow French government requirements to deliver heightened security checks to keep the travelling public safe following the recent attacks in France.”  The local Kent Police force said there was a 12-mile tailback, which it put down to a “vast volume of holiday traffic”.
People were advised to bring food and drink supplies, while a Sikh humanitarian organisation delivered water and snacks.
Xavier Czerwinski, a senior official from the Pas-de-Calais area, said: “The situation is exceptional because it’s the weekend when Britons make the great getaway to the continent.
“We have deployed the maximum resources.
“Given the European context and the prolonged state of emergency, officers are obliged to check every vehicle rigorously.”
P&O Ferries sought to reassure motorists who had already missed their allotted ferry, tweeting: “Rest assured, if you are stuck in the queues at Border Control in Dover we will put you on our next available sailing at no extra cost.”
Sikh relief organisation, Khalsa Aid, which supplies aid to refugees in makeshift camps, found itself helping motorists. The organisation was given a blue light escort to distribute 5,800 bottles of water and cereal bars to those stranded.
Aid worker Ravi Singh organised the drop after seeing images of the traffic on social media. He told Sky News the organisation normally works in the refugee camps where there is no water. He said: “And this is Britain, and I think the government should really have prepared for this, especially on a day like this, on a hot day, to provide some sort of reassurance if this happens there is a plan B.”  The Conservative MP for Dover, Charlie Elphicke, who was himself stuck in traffic for about two hours on Friday, said there had been a lack of forward planning that led to “poor transport management”. He called for the government to apologise for the “traffic nightmare”.
The shadow home secretary, Andy Burnham, accused the government of being “caught ill-prepared once again” and said the prime minister should have expected heightened security checks in France.
Many travellers vented their frustration on Twitter.