The warning issued by the port authority was echoed by shipping company P&O as the summer holiday season got underway, with thousands of families traveling to Europe this week after the end of the school year. The ferry from the port of Kent is the most popular sea route to France and many other parts of continental Europe. In a sign of growing tension over border management, Dover issued a furious statement overnight, accusing the French border force of failing to turn up in sufficient numbers to staff Dover’s passport booths — despite attempts to schedule a of the busiest holiday weekends of the year. The port said it was “deeply disappointed” by the level of resources committed by the French Police aux Frontières (PAF), which it described as “woefully inadequate to meet our projected demand” after only half of the nine wards Dover’s passports were open for early morning traffic. But by mid-morning on Friday, all booths were fully staffed, with the worst of the morning backlog beginning to clear. French officials in the northern region’s prefecture on Friday blamed “an unforeseen technical incident” at the Eurotunnel which they said caused the late arrival of border police in Dover. This delayed the opening of all kiosks to 9.45am. instead of 8.30am, leading to a traffic backup. Asked to provide more details, the prefecture declined. Getlink, the tunnel’s operator, said a power cable had been cut at about 7.30am, requiring them to carry out repairs and reduce service for a short time. But he dismissed the idea that the incident caused the delays at Dover. Dover’s complaint about the lack of French border staff was echoed on Friday by their counterparts in Calais, who said the lack of UK Border Force staff was also causing unnecessarily long waits on the French side of the Channel. Jean-Marc Puissesseau, chief executive of Port de Boulogne-Calais, said he had warned of staff shortages at the UK border for “several months”. “I think the PAF is being careful about this and they are trying to get more personnel to Dover. But I have asked for reinforcements from the UK BF — we need 50 per cent more people to ensure the port runs smoothly,” he added. John Keefe, public relations director at Getlink, which operates the Channel Tunnel, said the tunnel was running smoothly on Friday morning but that UK passengers had to adjust to a new post-Brexit reality. “Everyone needs to realize that there are now different types of border controls, so the time it takes to get through the border is longer – that’s a function of the UK being a third country in the EU,” he said. Channel delays are becoming more frequent, affecting local road systems in Kent, which are a key artery for goods and passengers. The Port of Dover handles approximately 2.1 million trucks, 2.8 million cars and 16 million passengers annually. The UK Home Office did not respond to a request for comment.

In a separate but further sign of strained EU-UK relations, the European Commission said it was expanding legal enforcement proceedings against Britain in a long-running dispute over post-Brexit trade arrangements for Northern Ireland. Announcing the measures to enforce elements of the so-called Northern Ireland Protocol covering customs, VAT and excise duties, Brussels said it was acting because of the UK’s “reluctance to engage in meaningful discussion” on the protocol since February. The commission said it had suspended proceedings a year ago in a spirit of cooperation but had restarted them because the UK government’s plans to pass legislation that would unilaterally seize the protocol was “directly against that spirit”. In response, the UK government described the panel’s decision as “disappointing”, adding: “A legal dispute is in nobody’s interests and . . . the EU is no worse off as a result of the proposals we have made in the Northern Ireland Protocol Bill.” Additional reporting by Sam Fleming in Brussels