Motorists face more misery on the roads to Dover as queues continue amid disruption expected to last until Monday.
Some people were forced to spend the night in their cars after getting stuck in jams leading to the port.
UK Border Force officials have been drafted in to work with French border police after the Government admitted motorists had suffered “extraordinary disruption”.
On Sunday morning Kent Police said people could expect delays of 10 hours on the A20, with around 12 miles of queuing traffic back to junction 11 of the M20.
Queues have eased slightly, authorities at the port said, but are likely to continue as more people set out to try and make the crossing to France.
Kent Police said the disruption is down to a “vast volume of holiday traffic” coupled with delays caused by heightened security at the border in the wake of terror attacks.
Increased checks were put in place by French authorities at the port in light of recent terror attacks, but questions have been raised about staffing levels to deal with the huge number of people travelling at this time.
After complaints that just one French officer was available to check in coaches on Friday night into Saturday, port authorities said six booths - four for cars, one for coaches and one for freight traffic - were manned overnight into Sunday.
The Home Office said UK Border Force officials are in place to help but added they cannot say how many as they do not go into “operational details”.
The Government said Kent police will also be “proactively managing” traffic to get drivers through more quickly.
A Government spokeswoman said: “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 border police) with border checks to remove the backlog.
“We understand that there has been extraordinary disruption in the Dover area today but safety is paramount.
“Measures are also being taken on the approach to the port where Kent Police will be proactively managing traffic to speed up the process.”
People travelling, many heading off for a summer break, spent up to 15 hours at a standstill in queued traffic while water supplies were dropped along the jam by police helicopter on Saturday.
A Sikh humanitarian relief organisation also pitched in with the effort, delivering nearly 6,000 bottles of water along with snacks to the stranded motorists.
Conservative MP for Dover Charlie Elphicke, who was stuck in traffic for around two hours on Friday evening, said there had been a lack of forward planning which led to “poor transport management” and urged the Government to apologise for the “traffic nightmare”.
Shadow home secretary Andy Burnham accused the Government of being “caught ill-prepared once again”, warning the Prime Minister should have expected heightened security checks in France.
Among those affected by the disruption was multiple sclerosis sufferer Tanya Cudworth whose journey to Dover from Tunbridge Wells took 20 hours.
The 50-year-old, who was travelling to a Frankfurt clinic to undergo stem cell treatment for her condition after raising £5,000 for the trip, described the experience as “absolutely horrendous”.
P&O Ferries said passengers will be booked on the first available sailing when they arrive at check-in.
Eurotunnel said there is a waiting time of around an hour to check in at the Folkestone terminal and a further 30 minutes on the terminal.
Those setting off on journeys on Sunday have been advised to bring food and water supplies.
Asked when the situation is likely to improve, a spokeswoman for the Highways Agency said: “Based on historic traffic patterns from previous years, we expect demand to subside from mid-afternoon on Sunday.
“However, that does not take into account the effects of the extra security checks at the port, so is only an indication.
“We also expect that next weekend will be busy, but not as busy as this weekend.”
Earlier, one Yorkshire traveller, Emily Knaggs, 30, from Rothwell, Leeds, told The Yorkshire Post she and her friend Amy Roberts had taken an hour to travel a mile on the approach to Dover.
She said: “We have spent three hours on the motorway and we are still four-and-a-half miles from Dover.
“We came down on Friday night and stayed in Canterbury overnight and set off at 7.30am on Saturday. We have spent the last three hours looking at the back of a lorry. It’s so frustrating.
“We are going to the Champagne region of France for a holiday. We will get there eventually but it is taking for ever.”
Traffic showed signs of easing as day broke on Sunday, but the Port of Dover warned of waiting times of nearly three hours from Roundhill Tunnels at Folkestone, around eight miles.
Once in the port motorists faced a further 90 minutes to reach the French border checks.
Meanwhile, a multiple sclerosis sufferer travelling to Germany for potentially life-changing treatment saw her dash to Dover turn into a 20-hour ordeal.
Tanya Cudworth, 50, was travelling to a Frankfurt clinic to undergo stem cell treatment for her condition after raising £5,000 for the trip.
Along with her partner, Steve Deene, 53, she set off from Tunbridge Wells at 8.30am on Saturday after waking to news of increasing delays at Dover.
The couple, from Derby, did not make it onto a ferry until 4.20am on Sunday.
Ms Cudworth described the experience as “absolutely horrendous”.
She said: “I’m taking the trip to get this treatment that I hope will keep me from having to go in a wheelchair. It’s not available on the NHS and we’ve done some fundraising. It’s a good job I didn’t have to be at the hospital sooner - 19 hours in the car has obviously aggravated my symptoms.”
Because of her condition Ms Cudworth, who works for Marston’s brewery, had to travel by road. She hoped to nip to Dover, take a short sail across the Channel and complete the final six-hour drive to Frankfurt on Saturday ahead of her Monday appointment.
However chances of them making the 10.30am ferry soon vanished as they found themselves stranded in a virtual carpark on the A20.
She said: “During the day it was so hot and there was nowhere near enough water and at night it was pitch black so you didn’t know what was going on around you. You couldn’t sleep because you had to keep moving forward.
“We didn’t get any water until 3am and I saw women with babies, young families and people with pets with no water. It’s shocking that more wasn’t done to get it to people, the authorities weren’t anywhere to be seen.
“My partner has been a lorry driver since he got his licence and he has never seen anything like it here or abroad.”
As the situation became desperate the couple decided to turn off the A20 and head for a hotel, but found everywhere was fully booked.
In the end they decided to grit their teeth and carry on crawling towards the port.
The Government said the “extraordinary” delays were down to a combination of high volumes of holiday traffic and extra security checks by French officials.
However Ms Cudworth suspected the official line may be hiding a different reason for the travel chaos.
“I don’t know whether the French are just annoyed with us because of Brexit or we are blaming the French for the delays.
“There’s a chance I will have to come back to Frankfurt for the treatment. If I do I will just have to fly.”