The head of the Port of Dover has said it is "absolutely true" that Brexit is the main cause of the chaos at the border over the weekend.
Thousands of holidaymakers and HGV drivers were forced to queue for hours on Friday as they attempted to board their ferry to France. There were also long queues on the roads approaching Eurotunnel’s Folkestone terminal at the weekend.
The port was forced to declare a "critical incident" after it was overloaded with traffic which clogged up most of Kent's major roads.
Rishi Sunak and Liz Truss have both blamed French officials for the delays, claiming that Britain's decision to leave the EU is not the reason for the mammoth queues.
However, asked if Brexit was to blame for the delays, Port of Dover boss Doug Bannister told LBC: "That is absolutely true, and indeed that was a primary planning assumption that we all worked towards for coming up with the summer plan.
"We knew what the checks were going to be like, we've been operating this way since we left the European Union."
He said they'd been planning for months for an event like this and that one of the main reasons for the delays is the extra time it takes to process people through the port now that the UK does not share freedom of movement with France.
When the UK was in the EU the only check required to enter France via a ferry was a quick passport inspection. Often that rule would be relaxed by officials if queues were building up.
Following Brexit, the UK is now treated by EU states as a "third country", which means border officials are obliged to take passports and stamp them.
This means each vehicle passing through border control takes more time to get through border inspection - with travel expert Simon Calder saying that can mean up to three times longer.
Other checks that can take longer include checking that travellers have enough money for their visit; accommodation to stay in; and a ticket to leave the EU.
Watch: British Ports Association denies Liz Truss' claim Brexit isn't causing Dover chaos
Calder added it was "absolutely not the case" that French officials are deliberately taking too long, though it does appear there was some initial understaffing at checkpoints.
The government has insisted changes to border control measures after Brexit did not have a “significant role” in the disruption at Dover, reiterating its stance that problems occurred because French authorities did not provide enough border officials on Friday during what was a peak period of travel.
Foreign Minister and Tory leadership hopeful Liz Truss said at the weekend that the issue was caused by French authorities not putting enough people on the border.
Sunak said: "The situation needs to be urgently addressed by the French. They need to stop blaming Brexit and start getting the staff required to match demand."
Last weekend was the busiest period in the school summer holidays, but this coming weekend is often the second busiest so there are fears the delays could be repeated.
Toby Howe, senior highways manager at Kent County Council and tactical lead at Kent Resilience Forum told the BBC the rest of this summer could be impacted by the queues, adding "basically it’s a very vulnerable situation, it takes very little to cause further issues."
On Monday queue times at the port had dropped from around six hours to one. Ferry operator DFDS has asked people to arrive two hours before their departure time to ensure they get on their boat.