Former Tory leader Lord Howard's suggestion that Theresa May would be prepared to go to war over Gibraltar has been dismissed as "apocalyptic" by the chairman of the Intelligence and Security Committee.
Critics have condemned the peer's comparison of the situation on the Rock to the Argentine invasion of the Falkland Islands, and ISC chairman Dominic Grieve said there was "no evidence" for Lord Howard's remarks.
Prime Minister Mrs May vowed not to trade away the Rock's sovereignty in pursuit of a trade deal with the European Union as the UK withdraws from the bloc.
The issue of Gibraltar was raised in draft EU negotiating guidelines circulated by European Council president Donald Tusk, which indicated Madrid would be given a veto over the British overseas territory's participation in a future deal.
The Prime Minister spoke to Gibraltar's leader Fabian Picardo to tell him the UK remained "absolutely dedicated to working with Gibraltar for the best possible outcome on Brexit".
While there was no reference to Spain's claim to sovereignty in the EU document, the specific mention of a role for the Madrid government in deciding whether a trade deal would apply to the Rock has caused unease in Westminster.
In a series of television interviews, Lord Howard repeatedly compared the situation to the Argentine invasion of the Falkland Islands which led to war with the UK.
He told Sky News's Sophy Ridge on Sunday: "Thirty-five years ago this week, another woman prime minister sent a taskforce halfway across the world to defend the freedom of another small group of British people against another Spanish-speaking country, and I'm absolutely certain that our current Prime Minister will show the same resolve in standing by the people of Gibraltar."
Asked if he was "seriously suggesting" going to war with Spain, Lord Howard told Channel 4 News: "Of course not," but he blamed the EU for the row and added: "I can see no harm in reminding them what kind of people we are."
Senior Tory Mr Grieve, who chairs the ISC, which oversees the work of Britain's spies, said: "I don't think I would have expressed myself in the terms that Michael Howard did, because it sounds a little bit apocalyptic. We have no evidence at the moment that the Spanish government would seek to invade and take over Gibraltar.
"That said, it is right to point out that with all our overseas territories, and that includes Gibraltar, if they were ever to be attacked we would go to war. That is stated United Kingdom Government policy."
On BBC Radio 4's Westminster Hour he added that Brexit could cause difficulties in the relationship with Spain, and criticised the EU for the "rather dangerous and slightly risky" decision to mention Gibraltar in the draft negotiating text "because it is likely to raise the temperature in what is going to be a difficult negotiation".
In an effort to provide reassurance to Gibraltar, Downing Street said Mrs May "reiterated our long-standing position that the UK remains steadfastly committed to our support for Gibraltar, its people and its economy" in her call with Mr Picardo.
A Downing Street spokeswoman said: "The Prime Minister said we will never enter into arrangements under which the people of Gibraltar would pass under the sovereignty of another state against their freely and democratically expressed wishes, nor will we ever enter into a process of sovereignty negotiations with which Gibraltar is not content."
Spain has a long-standing territorial claim on Gibraltar, which has been held by the UK since 1713 and has the status of a British overseas territory.