It’s staggeringly big business in Spain, where demand is being met by traffickers. Can a groundbreaking team turn the tide?

On a sunny morning in Madrid, two young women duck down a side street, into a residential block and up to an apartment front door. Then they start knocking. Marcella and Maria spend a lot of time banging on doors and yelling through letterboxes all over the city. Most of the time, these doors never open. When they do, the two women could find themselves in trouble. Their job on the frontline of Spain’s fight against sex trafficking is a dangerous one; both have been assaulted and threatened. Yet they keep on knocking, because they have been on the other side of those doors, forced to sell their bodies for a handful of euros, dozens of times a day, seven days a week.

To say that prostitution is big business in Spain would be a gross understatement. The country has become known as the brothel of Europe, after a 2011 United Nations report cited Spain as the third biggest capital of prostitution in the world, behind Thailand and Puerto Rico. Although the Spanish Socialist party, which two weeks ago won another term in government, has promised to make it illegal to pay for sex, prostitution has boomed since it was decriminalised here in 1995. Recent estimates put revenue from Spain’s domestic sex trade at $26.5bn a year, with hundreds of licensed brothels and an estimated workforce of 300,000.