Heathrow Airport is considering contingency plans to divert aircraft to other U.K. airports or EU hubs if queues at the border become too long.
The airport has seen queues of up to six hours at the border over the last few months as the number of checks and paperwork for U.K. arrivals increased.
The airport’s chief operating officer has previously warned passengers could be held on planes to prevent crowding. This would take measures a step further as a potential last resort.