Spanish foreign minister Alfonso Dastis likened the British Overseas Territory of Gibraltar to modern-day colonialism.
He said, just as in the fight over Catalonian independence, self-determination of the people of Gibraltar would only go so far.
The Spanish minister told Sky News’ Niall Paterson Britain would only ever regain its territorial integrity by taking back Gibraltar in the future.
The shocking remarks came up during a televised discussion on Catalonian independence as fervent supporters push ahead with the banned referendum despite the continued crackdown from the Spanish Government.
Police in the region have confiscated thousands of voting slips, and courts have fined and threatened to arrest regional officials in Catalonia.
Paterson questioned the foreign minister as to whether the Madrid Government felt territorial integrity was supreme over the views of the people who live in Gibraltar and Catalunya.
Mr Dastis said the two cases were completely different, but insisted Spain would not tolerate people challenging its territorial integrity.
He told Paterson: “The existence of a colony in Europe in the 21st century is an anachronism. We want to get back our territorial integrity.
“This debate comes from the 18th century – it’s a remnant of a bygone time. A matter of colonialism.
He added Spain would never drop its claim over Gibraltar and warned the territory’s tax model did not follow international standards.
Mr Dastis also spoke out against the idea of deliberately offering Britain a bad deal in the Brexit talks.
He added despite disagreement over Gibraltar, this would not impact Brexit talks.
He said: “We are not out to punish the UK because it would be tantamount to punishing ourselves.
“The UK is the first destination of our foreign investment and over a million Brits come to Spain every year.
“What we want is a successful Brexit.”
The Spanish official also dismissed any idea that a good Brexit deal would risk other countries following the UK out of the bloc.
He explained: “There is absolutely no threat of contagion here. In countries that would be tempted to follow Brexit – such as Denmark and Sweden – support for the EU has increased following the referendum.”