GETTY The RAF aircraft transporting Phillip Hammond to Gibraltar was barred from flying over Spain

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The Foreign Secretary was making an official visit to extol the virtues of remaining in the EU when the diplomatic slap in the face took place last week. It comes just a week after a US nuclear submarine threatened to ram a Spanish ship in a shocking incident of provocation. In the latest aggression, Spanish authorities ordered the plane off its airspace despite being told Hammond was onboard.

It is shameful that Spain is treating a Nato ally in this fashion Andrew Rosindell

Spain has routinely banned all British military planes from flying over or landing there since 1989 if their final destination is Gibraltar, as part of its protests over the Rock’s sovereignty. However, official sources confirmed that Spanish authorities had been informed this flight was carrying the Foreign Secretary. The jet was, nevertheless, still forced to by pass Spain and fly over Portugal.

The visit also prompted Spanish Justice minster Rafael Catala to snub a Downing Street reception on the eve of David Cameron’s anti-corruption summit.

Mr Hammond warned Gibraltarians the UK would no longer be able to protect its interests if they voted to leave the EU in June 23 referendum. But last night Andrew Rosindell MP warned that if Gibraltar voted to remain, it would find itself part of the EU region of Andalucía within a decade. “It is sad that, even with a majority Conservative Government, our Foreign Office continues to pussy foot around Spain instead of slamming the door in its face. “As long as Britain continues to give the impression that we are not a hundred per cent committed, that there is room for negotiation over sovereignty, the Spanish will continue to behave as they are behaving and relations will remain low.

GETTY Spain has threatened to close its border with Gibraltar in the event of Brexit

“It is shameful that Spain is treating a Nato ally in this fashion, yet all we do is to send diplomatic notes or call in the Spanish Ambassador.” Gibraltar is likely to vote to Remain in June’s EU referendum, with one Government source admitting: “Frankly, the EU has done more to control Spain’s behaviour than the Foreign Office – though, admittedly, that’s not saying much.” Madrid has also threatened to close its border with Gibraltar in the event of Brexit, a reminder of the siege ordered by Spanish Dictator General Franco which lasted from 1969 to 1982, long after his death.

CROWN An US nuclear submarine threatened to ram a Spanish customs vessel unless the Royal Navy intervened

In a warning to Gibraltarians, however, Mr Rosindell, Chairman of the British Overseas Territories and Crown Dependencies All Party Parliamentary Groups, said: “I think the message to Gibraltar should be that in the next decade Britain could become so diminished within the EU that we no longer have the might and sovereignty to defend Gibraltar. “The shortsighted view by some in Gibraltar is going to backfire. Europe will be regionalised and Gibraltar will become part of the Andalucían region. “Spain will win in the end via the EU."

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Britain is not the only nation to feel frustration at the hands of Spanish provocation in recent days. Last week the Sunday Express revealed how the Captain of a US nuclear submarine threatened to ram a Spanish customs vessel which was blocking its entry into British waters in Gibraltar. The threat caused the submarine’s single escort, a small Royal Navy patrol boat, to fire flares across the custom boat’s bows. Now the US may formally express its concern at Spain, a Nato ally, extending safe harbour to 57 Russian submarines and naval vessels at its North African enclave in Cueta since 2011.

GETTY Gibraltar is likely to vote to Remain in June’s EU referendum