Britons flying to Gibraltar from the UK will now have to go through the EU’s controversial electronic border system (EES) as a new UK‑EU treaty takes effect. Gibraltar, Britain's only mainland border, will effectively join the Schengen area after midnight on Wednesday.

The EES, which uses fingerprint and face scans, was fully launched in April but has suffered technical glitches, leading to queues at some airports. Fabian Picardo, Gibraltar’s chief minister, warned that the new checks could cause delays, especially for families with children under 12.

Gibraltar’s airport handles about 300,000 passengers a year, most of whom come from the UK for holidays in southern Spain. Residents—38,000—are exempt from the system, but visitors registered elsewhere will move faster.

Spain won control of the EES checks in the treaty, and Spanish border police will operate a joint facility at the airport, dubbed the “Schengen shack.” The move keeps the land border open without passport controls, easing the flow of the 15,000 daily Spanish commuters and tourists.