* Biggest fall this year on adjusted basis
* British numbers down 7.5 percent on non-adjusted basis
* U.S. to take Spain's spot as world No.2 destination
* Tourists switch out of hotels towards cheaper options
MADRID, May 21 (Reuters) - The number of tourists visiting Spain continued to fall in April, even though the busy Easter holiday season fell in that month this year, official figures showed on Thursday.
Tourism is Spain's second most important industry after the now-crumbling construction sector and generates 11 percent of gross domestic product.
Unadjusted data showed foreign visitor numbers slipped 1.7 percent in April year-on-year as the economic crisis in Britain in particular brought despair for hoteliers, restaurants and airlines here.
Stripping out the effect of the Easter break -- which fell in March last year -- arrivals fell 11.8 percent, the worst drop this year, to 4.5 million.
Figures from the tourism ministry also showed that holiday-makers were turning away from hotels and opting for cheaper apartments and campsites, worried about surging unemployment across Europe and the global economy.
Figures from the World Tourism Organization shows the United States stole Spain's spot as the world's second most visited destination last year, relegating it to third spot, with France in first.
A sharp fall in the value of the pound against the euro in recent months has made Spanish holidays more expensive for Britons, and unadjusted data showed a 7.5 percent fall in the number of British tourists in Spain.
However, the number of Germans -- Spain's second most important market -- grew 3.2 percent, while visits from Belgium, Italy, Switzerland and Nordic countries also rose.
Hotel owners are slashing their rates by up to 40 percent as they try to keep rooms full. However, ministry data shows 12 percent fewer foreign tourists chose to use them. The number of visitors choosing apartments, campsites and other non-hotel options jumped 19 percent compared to April last year. (Reporting by Ben Harding; Editing by Ruth Pitchford)