LONDON — Travelers arriving in the U.K. faced hourslong delays Saturday after a technical problem shut electronic border gates at airports across the country, forcing everyone to have their passports checked manually on what was expected to be one of the busiest travel weekends of the year.

The Home Office, the government agency responsible for immigration and borders, said it was working to correct a “nationwide border system issue,” though it provided no details about what caused the problem.

Airport operators asked f …