An independent Catalan is in the UK's best interests, particularly during Britain's withdrawal from the European Union, a former British diplomat has said.
In a letter to The Financial Times, Charles Drace-Francis said "it is in the permanent interests of the UK to prevent Iberia from being dominated by Madrid."
The retired diplomat went on to list several historic reasons why Britain should support Catalonia's bid for independence from Spain.
"If the Catalans had not revolted in February 1640, Portugal would not have been able to regain its independence — very few British people realise that Philip II of Spain gobbled up Portugal in 1580 and the Armada was launched mainly from Lisbon," he wrote.
"Moreover, Catherine of Braganza would probably not have married Charles II and Britain would not have prospered as we did.
"Again, if the Catalans had not supported the Archduke Carlos in the War of the Spanish Succession, Prince Georg of Hesse-Darmstadt would probably not have been able to seize Gibraltar — and more importantly hang on to it."
Mr Drace-Francis added: "Although we abandoned the Catalans in 1713 and in 1938, they gave us much support in helping escaped British aviators in 1940-44 at a time when it took six weeks to build a bomber but six months to train a pilot.
"And also helped many others, notably Jews and artists, escape from the Nazis."
He concluded: "In short, an independent Catalonia is in the best interests of the UK, especially at a time when our relations with other European nations are so fraught."
Spain's Prime Minister has urged Catalonia's leader to "act sensibly" and renounce its independence bid in order to head off a threat by Madrid to impose direct rule.
Mariano Rajoy appealed in the national parliament, where he sought to win more political support for his threat to take direct control of Catalonia unless the rebel regional government drops its secessionist plans.
It would be the first time in Spain's four decades of democracy direct rule has been imposed.
Catalan's leader Carles Puigedmont has already defied Madrid once this week, reiterating an ambiguous independence declaration he made last week and immediately suspended.
Thursday's deadline is Mr Puigdemont's last chance to abandon an independence declaration which Madrid has rejected as illegal.
"It's not that difficult to reply to the question: has Catalonia declared independence?" Mr Rajoy asked in parliament. "Because if it has, the government is obliged to act in one way, and if it has not we can talk here."