Getty ImagesBritish travellers to Gibraltar would have to show their passports to Spanish border guards, under a deal with the EU to remove checks at its land border with Spain.
Details of a new system of dual checks at the Rock's airport and port have been confirmed in a draft treaty published on Thursday.
The agreement is designed to bring certainty to the British overseas territory nearly a decade after the Brexit vote threw its status into doubt.
Pressure to reach a deal had been mounting ahead of the full application of new checks on passengers entering the passport-free Schengen zone in April.
Under the deal, Gibraltar will not officially join the zone, made up of 29 mainly EU countries including Spain.
Instead, Spanish authorities will carry out "second line" Schengen-style border checks in a special zone, after border checks conducted by Gibraltarian officials.
Spanish guards will have powers to arrest, search and interview travellers "where it is justified in the course of border control," according to the treaty.
The system should eventually allow for the removal of border infrastructure at Gibraltar's land border with Spain, which is crossed every day by around half of the Rock's workforce.
The UK government is likening the new system to that in operation at London's St Pancras station, where Eurostar passengers are checked by both British and French officials before boarding trains for the continent.
British nationals make up a huge share of visitors travelling to Gibraltar for tourism, representing 86.5% of all departures from its airport in 2024, according to the territory's most recent tourism survey.
Since Brexit, Spain has allowed Gibraltar residents to cross the border without having their passports stamped, but there have been periodic complaints from Gibraltar about Spanish police tightening checks.
From April, Spain had been due to apply the EU's new automated border system, including biometric checks, at the border with Gibraltar, which the UK says would "devastate" Gibraltar's economy.
Gibraltar's chief minister Fabian Picardo has welcomed the agreement, adding it delivers "the certainty our people and businesses need".
Speaking in the Commons, Foreign Office minister Stephen Doughty said the deal was evidence of a "new era of co-operation" with the EU since Labour took office.
His Conservative shadow Wendy Morton said the treaty required "proper scrutiny" and questioned how "operational overreach" from Spanish police could be avoided.
The government also says a majority of goods destined for Gibraltar will be cleared by EU customs offices in Spain, in a deal designed to avoid the need for customs checks at the land border.
Gibraltar was not covered by the UK's 2021 trade deal with the EU, and the UK has previously described it as the "last piece of the EU exit jigsaw".
The treaty implements a political deal agreed between the UK and EU in June last year, and confirms key details of how the new arrangements will work in practice.
It has been published in draft form whilst legal teams complete final reviews and translation of the text. It will have to be ratified by both the UK and European Parliaments.
