Aerial view of the delays at UK's Dover port

STORY: Ferry operators warned passengers travelling to Calais they faced delays of up to four hours at the start of what is typically one of the busiest periods of travel as schools break up for their summer holiday.

Port of Dover CEO Doug Bannister has declared the situation a 'critical incident', a spokeswoman told Reuters. They did not specify what that declaration meant in practical terms.

Graham Stuart, Britain's minister of state for Europe, told Sky News that the government had been working with France to clear the backlog.