London's mayor says long delays for passengers arriving at the city's largest airport risk damaging Britain's reputation as it hosts the Olympics.
Boris Johnson on Monday wrote to Home Secretary Theresa May amid increasing concerns over lengthy lines at border control desks for those arriving at Heathrow Airport.
Passengers have complained of long delays, on some occasions of more than an hour, because of lengthy passport and visa checks and a lack of border staff.
Johnson said the delays were giving "a terrible impression of the U.K." and demanded action.
Lawmakers and Heathrow's operator BAA Ltd. have already called for additional border staff.
Heathrow typically handles an average of 190,000 arriving and departing passengers each day.