By Ellen Emmerentze Jervell 

FRANKFURT--Britain won't officially leave the European Union for at least two years, but European tourism officials already fear a British exit this summer.

The reason: A fall of roughly 6.6% in the value of the British pound against the euro Friday, after Britons voted to leave the EU. Currency traders, who were surprised by the referendum's outcome, dumped sterling on fear of looming U.K. economic troubles.

International Consolidated Airlines SA, the parent company of British Airways and Spain's Iberia quickly issued a profit warning, blaming market volatility. A big question businesses face now is whether the pound will remain depressed, upending economic relations between Britain and its trading partners.

At the front lines of those relations are international tourists paying for hotels, meals and taxis in foreign currencies. EU destinations accounted for more than two thirds of British foreign travel, according to Euromonitor International. Spain, France, Italy and Germany are among the most visited countries.

Merrion Charles, a British woman who runs her own high-end Italian travel consultancy from Tuscany, said British tourists are a key source of income for her business. She feared the consequences of the U.K. exiting the EU could be "huge" for her business.

"A weakened pound, inevitable complications regarding ease of travel, economic impact and the concerns of a lot of Brits will, I believe, lead to a significant downfall in clients from the U.K.," she said, adding, "I hope and pray I am wrong."

According to Italian tourism association Federturismo, about 12 million British tourists take a vacation in Italy every year, making them one of the largest groups of holidaymakers in the country.

Federturismo Chairman Renzo Iorio said Friday that "everyone was sure that the Remain would have won," and that Italian tour operators thus hadn't yet considered any special action to promote tourism in the coming few months.

"We'll compensate with other nationalities or by throwing into niche markets," he said Friday.

The consequences of a British departure, in particular a devaluation of the sterling, could reach far across Italy's borders. Britons for instance represented 22% of total visitors to Spain between January and April of this year, according to the most recent figures from Spain's statistics agency.

Teneo Intelligence, an advisory firm in New York, said the Greek economy would be particularly vulnerable to the economic impact from a British exit from the EU. More than 2 million British tourists visited the country last year, contributing around EUR2 billion to the country's tourism sector, they said.

Not all tourist operators were worried yet. Dimitris Giannakopoulos, managing director at the Athens-based villa rentals company White Key Villas, said the villa market in Greece "greatly" depended on British tourists but his clients were in the "very high-end segment."

If the pound remains depressed, Britons may prefer to stay at home for their vacations, said Wouter Geerts, travel analyst at Euromonitor. And even British tourists who venture abroad could spend less while traveling if the pound buys less. "U.K. residents will be more aware of their budgets," he said.

In the German capital of Berlin, Burkhart Kieker, chief executive of tourist organization VisitBerlin, said he was only "slightly worried" about the consequences of Friday's referendum. He predicted resilient tourism because "Berlin has a very positive image in the U.K."

Britons are the biggest tourist group in Berlin with 560,000 U.K. residents spending at least one night in the city last year. For now, Mr. Kieker said he was "breathing deeply, observing, and hoping."

At Germany's DER Touristik Group, CEO Soeren Hartmann said it was "safe to say" that a British exit from the bloc would not be positive for travelers in Europe.

He said officials in London and at the EU in Brussels should ensure that pan-European travel remained as uncomplicated as possible, adding, "new administrative barriers would spell disaster for the travel market."

Manuela Mesco in Milan and Jeannette Neumann in Madrid

Write to Ellen Emmerentze Jervell at ellen.jervell@wsj.com

(END) Dow Jones Newswires

June 25, 2016 09:11 ET (13:11 GMT)