IT has been billed “the book that revolutionised Catalonia” and whether or not that’s the case Operació Urnes (Ballot Operation) has been on the best-seller lists in the wealthy, north-eastern Spanish state since Christmas.

The book, written by Laia Vicenç and Xavi Tedó, journalists from the Catalan newspaper ARA, chronicles the clandestine campaign to make sure the ballot boxes for the October 1 independence referendum – which Spain declared illegal – were safely delivered to more than 2000 polling stations.

Tedó and Vicenç had extensive access to the mastermind of the operation – who went by the name Lluís – but his and the names of others have not been revealed; they used only the Telegram or Signal messaging systems to communicate, and no recordings were made. Interviews were written into notebooks.

Vicenç told The National about some of the problems they faced: “The Spanish government forbade the referendum, so people self-organised to get ahead with the vote. They used clandestine methods, like Telegram or Signal, which conditioned us, because people didn’t want to expose themselves and asked to do the interviews in person and not record.

“We only took notes in a notebook. Another complication was looking for people from different towns in Catalonia who had been involved in the operation, so the story had a territorial balance.

“The search for the people was not so difficult: people met us and took us to the others ... The most difficult was when we had to write the book, because we had only one month, and we did not stop working in the politics section of ARA, in one of the most politically intense months of recent decades.”

The book has been well-received – how do you and Tedó view the reaction to it?

“We are very happy. We could guess that there was a lot of interest in this topic, but even in our wildest dreams we did not think that Operació Urnes would be so successful. We think that it has done so well (38,000 books sold and 17 weeks in Catalan charts) because the referendum is the only victory of the independence movement.

“People ‘cling’ to this day to face the bad news of the recent months, such as the imprisonment of political leaders.”

What has been your experience of violence and intimidation by police?

“It was a disproportionate performance by the Guardia Civil and the Policía Nacional, as shown by the almost 1000 wounded. The Spanish government said the forces of the state fulfilled a judicial order, but ... I think they had to demonstrate in some way that it was trying to avoid the referendum, even by force.

“Since that day, nothing has been the same again, and there are many Catalans who have felt despised and insulted by the police, who are supposed to protect society. There are politicians who are not independentists who have recognised that police brutality will forever mark a before and after in the relationship between Catalonia and Spain, and that Rajoy broke all emotional ties with the Catalans.

“The violence by the forces of the state encouraged non-independentists to go to vote.”

In the foreword to the book, the authors say the “army of invisibles”, working underground, made the impossible possible – and they add: “Operació Urnes is, then, a tribute to all those anonymous heroes who collaborated because the referendum summoned by the government of the Generalitat, was the most important political event of the last decades in Catalonia, and they made it possible.”