GIBRALTAR — There is a troubling side story jutting into the Brexit debate from this tiny British territory at the southern tip of the Iberian peninsula.

Madrid-based daily El Mundo reports that in Gibraltar — affectionately known as "the Rock" — locals and the government alike are opposed to "Brexit", a British exit from the European Union, which is up before a national referendum this summer.

The territory, home to a British military base, has been under British control since 1704. Every day, around 10,000 workers cross the border from Spain to work in Gibraltar, which has open borders with Spain thanks to the UK's membership in the EU.

The Rock maintains its own autonomous parliament and fiscal regime, a solution that locals consider the best of both worlds between the UK and Spain, which still holds an outstanding claim to the territory.

But if Gibraltar's 30,000 inhabitants are dragged out of the EU by their compatriots 1,200 miles away — even if they vote to remain in their own local referendum — they will lose the right to free movement across the border to Spain, and trade will become subject to border controls.

"We are more protected within the EU," says Natasha Passano, a local schoolteacher, to El Mundo.

The debate has grown tense as Gibraltarians, known as llanitos, consider the repercussions a vote could have on their lives. "I will vote to remain in the EU," says Daniela Caruana, a pharmacist. "My boyfriend works here but he is from across the border, and we live in Spain because the rent is cheaper there."

Gibraltar's government is a strong supporter of remaining in the union, and Chief Minister Fabian Picardo recently warned that Brexit could rekindle the long-standing diplomatic conflict between Spain and the UK over ownership of the territory. Spanish authorities declared that if Britons were to decide to leave the bloc, the matter of sovereignty would have to be discussed immediately.

When British voters go the polls on June 23rd, they could decide the fate of this centuries-old possession. "I don't think the Spanish would erect a border fence," says a shopkeeper. "But we would be in limbo."