Spain forced a Red Arrows display in Gibraltar to be cancelled after it warned that it would be considered a "hostile act".
According to diplomatic cables seen by the Telegraph, an unnamed Spanish official warned that their country's response would "not be mild".
The Spanish official reportedly said that Spain considered the display “unnecessary, unconstructive and provocative” and that “this was not the time to undertake this sort of activity.”
According to the Telegraph, the exact Spanish threat was "more explicit", but was not disclosed by the publication.
Spain said the display would be a "hostile act"
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The British Embassy in Madrid suggested it was "clear that Spain is deeply opposed to the activity".
The UK however maintained that the event would mainly take place in British airspace and would not need approval from Spain, but backed down nonetheless.
A Ministry of Defence spokesperson said on the cancellations: "As part of operational planning, a variety of potential display dates and locations are considered by the RAF.
"A wide range of factors influence whether these are able to proceed."
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The UK however maintained that the event would mainly take place in British airspace
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A prospective visit by HMS Queen Elizabeth to The Rock was also reportedly scrapped in order to "appease" Spain, the Telegraph revealed.
Another leaked cable reportedly claimed that Governor of Gibraltar, Vice Admiral Sir David Steel, was "conscious" that several events in recent years had been "turned off" in order to appease the Spanish.
He said: “I am also conscious that we have turned off a number of events over the last three years (not least a visit of HMS Queen Elizabeth) just to appease SP [Spanish] sensitivities.
"In return we have gained very little – just more demands.”
Gibraltar has been a spot of contention following Brexit
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The Governor added: "If we back down now we will once again show a weakness that the Spanish will undoubtedly exploit."
It comes amid recent tension over the status of Gibraltar - a British Overseas Territory - exacerbated following Brexit.
Margaritis Schinas, a Vice-President of the European Commission, caused controversy when earlier this month he claimed Gibraltar "is Spanish".
José Manuel Albares, Spain's Foreign Minister however dismissed the comments as "incomprehensible".