Brits have been warned that long queues at the border risk becoming the "new normal" amid a mounting blame game over days of gridlock at Dover.
Holidaymakers and lorry drivers have been caught up in travel chaos in recent days, with bumper to bumper traffic leading up to Britain's busiest passenger port.
Traffic finally began to ease on Sunday, with queues of around an hour to get through, a port spokesman said.
Post-Brexit border checks and a shortage of French officials at checkpoints in Dover have been blamed for the delays, stoking fresh tensions with Paris.
Lord Ricketts, a former ambassador to France, warned that the delays were an inevitable outcome of post-Brexit bureaucracy.
“The shortage of French border force officials is a short-term, tactical problem,” he told the Observer.
“The long-term, serious issue is that this is the first time we’ve seen the full pressure on the border after Brexit.
"Even if it was a full complement of the French border force there would still be massive delays, because Dover port can’t cope with the volume.
“The underlying reality is that no matter how many they have, given the size of the port, given the fact that the government failed to invest in expanding the facilities, it is going to be like this – this will be the new normal.”
Lord Ricketts called for cooperation with the French, adding: “Of course, the French will be watching this and will say, ‘yet again, we’ve become a political football in the party leadership issue’.”
Tory leadership hopefuls Rishi Sunak and Liz Truss have both blamed the French authorities for the delays.
Mr 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.
"It’s absolutely not acceptable to have families stranded in their vehicles like this."
Foreign Secretary Liz Truss spoke to French foreign minister Catherine Colonna on Saturday.
She said: "I was clear the French authorities have not put enough people on the border and we need to see action from then to resolve the terrible situation which travellers, including families, are facing."
Ms Colonna tweeted that the pair had a "good talk", adding: "We welcomed the cooperation between our competent technical services to reduce the delays. Need also to improve the facilities of the port of Dover."
French politician Pierre-Henri Dumont, Republican MP for Calais, told BBC News it was "an aftermath of Brexit" with more checks needed and claimed the Dover port is "too small".
Port chief executive Doug Bannister thanked travellers and Dover residents for their understanding during what he described as a "challenging period".
He said he was "incredibly grateful to everyone who has turned this situation around, from the French and UK authorities to our ferry operators, Kent partners and our own port staff".
A UK Government spokesperson said: “A shortage of French border control staff at the border in Dover, who control entry to France, and exceptionally high numbers of people travelling this weekend have led to roads in Kent becoming extremely busy.
"We are working closely with French authorities, the Port of Dover, Kent Resilience Forum and police to ease disruption and provide on-the-ground support.
“We strongly recommend passengers check the latest advice from their operators before travelling and, as with any long journey, ensure they have enough water and food provisions with them."
