A survey published on Monday revealed that 64 percent of Spaniards want Britain to remain within the European Union.
Spain leads as the nation most against Brexit according to a poll by Bertelsmann Foundation which showed that the average across Europe was 54 percent in favour of the status quo.
Spain was also the country which would be least likely to vote in favour or breakaway from the EU with a 74 percent claiming that they would vote to remain if offered their own referendum on membership, according to the poll.
On Wednesday, Pablo Iglesias, the leader of leftist Podemos, which is pro-European Union although against the austerity policies enforced by Brussels, urged British "comrades" to vote to Remain.
Pablo Iglesias - Podemos leader and candidate for Spain's next PM - urges Britain to vote Remain pic.twitter.com/lIWoaMQwah— Owen Jones (@OwenJones84) June 22, 2016
Brexit could derail Spain's fragile recovery
Spain has a lot to lose if trade links between the two countries are weakened.
Spain currently enjoys a €11 billion surplus in the trade balance with the UK, roughly 1.1 percent of GDP, according to El Pais.
The UK is also Spain's primary direct investment destination, with Spanish companies investing €48 billion (14 percent of annual total) there.
In return, around 10 percent of the UK's total foreign investment is spent in Spain.
Earlier this month Spain's most powerful business leaders warned of the dangers of Brexit.
An open letter to the FT signed by industrialists, including the CEOs of Spain's top companies, warned that Brexit “would reduce prosperity”.
Fashion giant Inditex, telecoms behemoth Telefónica, global energy firm Iberdrola, and construction company Ferrovial, alongside banks, Santander and Sabadell, which have all contributed huge investments in the UK, are all worried about the uncertainty Brexit could bring.
“While respecting the decision of the people in the United Kingdom, we believe that a Europe without the UK would be weaker, just as the UK itself would be weaker outside Europe,” they wrote. “We believe the case for Europe has never been stronger.”
Spain is one of the economies thought to be most vulnerable to the effects of a Brexit.
According to rating agency Standard and Poor's Brexit Sensitivity Index, Spain is ranked eighth on a list of economies with the most to lose.
“Spain has large financial and FDI exposures to the U.K., in particular through its large retail banking subsidiaries and telecom operations,” a report by S & P said.
Tourism industry could suffer
Millions of British tourists flock to Spain each year for their holidays. In fact Brits accounted for nearly a quarter of all vistors to Spain last year, contributing €14 billion to the Spanish economy.
While there is no reason to think that Brexit will put people off coming to Spain, experts predict that a drop in the value of sterling against the euro would take its toll.
“The impact of Brexit on tourism at least in the short term would be mainly due to the depreciation of the pound,” predicted Madrid-based financial consultancy AFI
Expats may have to go home
The biggest fear over Brexit lies among British expats in Spain and Spanish workers currently living and working in the UK. What could happen to their rights?
Acting prime minister Mariano Rajoy issued a dire warning earlier this month when he said "a Brexit vote could mean expats losing the right to live and work in Spain."
More than 400,000 British citizens officially live and work in Spain, in comparison to 100,000 Spanish citizens who live and work in the United Kingdom, he claimed.
Athough the true number of Brits residing in Spain is estimated to be as high as around one million. The worst case scenario is that they will have to apply for work permits and residency and may no longer be entitled to free health care.