Sky sources say the reports are credible and that British intelligence was involved in monitoring the suspects although that role was described as “minimal”.
The target in the British territory was said by El Pais newspaper to be the main shopping centre.
Three suspects are in custody. When police raided the home of one, Cengiz Yalcin, a Turk, near the border with Gibraltar, they found a video which was used in evidence against him.
A “significant” haul of explosives were also found as well as the parts for three paragliding machines.
The video is said to show him piloting a large remote-controlled plane. The aircraft drops two packages from the air to the ground at which point “Yalcin celebrated his achievement”, said El Pais.
The suspicion is the plan was to drop explosives on the shopping centre.
The two other suspects are both Chechen. All three men are thought to have connections with al Qaeda.
A judge detained Yalcin for “possession of explosive substances and devices with terrorist aims” and also held the two Chechen men, Mohamed Adamov and Eldar Magomedov, for belonging to a terrorist organisation and possession of bomb-making material.
Magomedov is thought to be a former member of the Russian special forces “Speznatz” unit and an expert in explosives.
His arrest follows co-operation between intelligence agencies in France, the US, the UK and Spain.