The EU is proposing that for the next four years, the European Border and Coast Guard Agency – or “Frontex” – would control the border during the transitional period. Spain and the UK struck a last-minute deal at the end of 2020 to avoid a hard border between the European nation and the sovereign territory.

       The deal allowed Gibraltar to become part of the Schengen area, and paved the way for the demolition of a 1.2km fence between the territory by moving border checks to Gibraltar’s port and airport.

       However, that agreement is not legally binding, and so in October negotiations began again between the two nations to secure a permanent, international treaty.

       The UK has refused to allow Spanish National Police and Civil Guard to control the border with Gibraltar as it would be “an attack on the sovereignty” of the UK.

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       The EU’s initial position in negotiations is that control of the border crossing at the port and airport of Gibraltar be given to the Spanish, with the functional role being taken over by Frontex for the transition period.

       It could then be decided whether to make it a permanent arrangement.

       The aim of this proposal is to “remove the physical barriers” between the territory and the European nation, so Spanish who work in Gibraltar could get through easier.

       However, it has concerned Spanish security forces, who see it as a concession on their sovereignty.

       Sources inside state security told El Espa？ol that this could become a permanent source of conflict with the UK.

       Additionally, last Wednesday José Ignacio Landaluce, mayor of nearby Algeciras, said: “Spain cannot compromise because even if it is for four years, with the British, you know that you give them an inch and they take a mile.

       “If the police and the Civil Guard are not allowed to control what enters Europe, in the end, in four years' time, it will not be possible at all.”

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       Spanish security sources could not rule out the possibility of double border control eventually being imposed.

       Frontex support was requested by the Spanish according to the agreement reached in December last year between Spain and the UK.

       The second round of negotiations on a permanent treaty is due to take place in London this week, starting on Wednesday.

       The initial agreement between the two countries made clear that it does not modify the position of either Spain or the UK regarding ownership of Gibraltar.

       Spain has near constantly claimed sovereignty over the rock since it was ceded to Britain under the Treaty of Utrecht in 1713, after it was captured by Anglo-Dutch forces.

       In 1967, in a referendum of Gibraltarians, 99 percent voted to remain British.

       Gibraltar's 1969 constitution states that there can be no transfer of sovereignty to Spain against the wishes of locals.

       A further referendum in 2002 of Gibraltarians resoundingly rejected the idea of joint sovereignty over the territory between the UK and Spain, with 99 percent voting against the proposal.

       Despite there being little desire in Gibraltar to accept Spanish claim, the Spanish Foreign Ministry’s budget this year still gives one of its priorities as the recovery of sovereignty over the rock.

       It said that the existence of “the colony of Gibraltar destroys the national unity and territorial integrity of Spain.”

       Additional reporting by Maria Ortega