The ongoing development relies heavily on imported Spanish stone and rock transported across the border through La Línea de la Concepción. Official figures show tens of thousands of tonnes of material have been moved to reinforce coastal works, including the flagship Eastside urban development.

The £1.1 billion project plans to transform the eastern coastline with 1,300 luxury homes, a 200-room hotel, commercial hubs, and a new marina.

Spain's main opposition party, the People's Party (PP), has submitted formal inquiries in parliament questioning why the government has taken no action to halt the project.

PP representatives claim the reclamation violates the 1713 Treaty of Utrecht, under which Spain ceded the Rock of Gibraltar to Britain without conceding territorial waters, air space, or land borders.

Local environmental campaigners from Verdemar-Ecologistas en Acción have also raised concerns over the environmental impact on the Eastern Strait conservation zone, warning that large-scale infilling risks damaging delicate marine habitats.

Gibraltar asserts rights over up to three nautical miles of surrounding waters, maintaining that land reclamation on its eastern side is a sovereign domestic matter.

The Spanish Ministry of Foreign Affairs has maintained its official stance that Spain does not recognise Gibraltar's jurisdiction over the waters, but critics argue the lack of diplomatic or enforcement action amounts to tacit approval.