In a strong warning against Britain leaving the European Union, Gibraltar’s chief minister Fabian Picardo has said a Brexit could have severe ramifications for Gibraltar, but that any form of joint-sovereignty with Spain would not be on the table.

Spain can stick joint-sovereignty "where the sun doesn’t shine", Mr Picardo has told The Independent.

Spain has become increasingly vocal in its claim to Gibraltar in recent years, with Spanish Prime Minister Mariano Rajoy describing Gibraltar as an “anachronism”, and “the last colony in Europe”.

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Now, Mr Picardo believes the Spanish government would make joint-sovereignty between Spain and Gibraltar “a prerequisite to Gibraltar having access to the single market” in the event of a Brexit.

Speaking to The Independent, Mr Picardo said: “The position in Gibraltar has not changed, will not change… Gibraltar will always be British."

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"Senor Margallo [the Spanish foreign minister] has been explicit in saying he would be putting the issue of joint-sovereignty for Gibraltar on the table as a prerequisite to Gibraltar having access to the single market in future.

“Well, you know what, he can stick that into his autobiography, or anywhere else where the sun doesn’t shine. It’s not going to prosper with the people of Gibraltar, and that’s on the record.”

He added: “Spain needs to wake up and smell the coffee. The Spanish government needs to wake up and smell the coffee. Gibraltar will never be Spanish.”

If Britain votes to leave the EU at next month’s referendum, it could pose serious problems for Gibraltar’s economy, which has boomed in recent years with rapid growth in its financial services sector and gambling industry.

Gibraltar’s economy is dependent upon a workforce of around 10,000 people who cross through the frontier with Spain every day.

In 2013, a major dispute over fishing rights saw Spanish border police impose punitive controls on movement in and out of Gibraltar, resulting in six-hour queues to enter and exit the territory through the single border crossing.

Gibraltar’s economy is dependent upon a workforce of around 10,000 people who cross through the frontier with Spain every day (GETTY)

If the UK leaves the EU, Mr Picardo said Gibraltar will no longer be able to depend on EU laws that ensure the right of freedom of movement.

Mr Picardo said: “In past years we’ve been able to avail ourselves of our rights under the treaty of Rome… We lose the right to use that legal lever against Spain if we leave the European Union. That is what’s under threat.”

Speaking about fears Spain could again curtail movement in and out of Gibraltar, Mr Picardo said: “The only person who thought it was a good idea previously to close the frontier between Gibraltar and Spain was the fascist dictator General Franco. So I don’t know why it is that [the Spanish government] needs lessons from a deceased dictator."

What to believe about the EU referendum

Asked if he believed David Cameron is fighting effectively to keep Britain in the EU, Mr Picardo said: “The prime minister and I are part of the same team. We’re making the same arguments.”

He added: “The Brexit camp is no longer making the economic argument because the remain camp has won the economic argument every single day since the referendum was called.”