The left and the right of the political spectrum are at odds with each other after the March 11 attacks in Madrid. Conspiracy theories abound in this latest installment in the ongoing conflict between traditionalists and progressives that can be traced back to the Civil War and Carlist Wars before that.

Following the death of Franco, the fledgling Spanish democracy of the late seventies and early eighties was prepared to overlook many of the appalling political crimes that took place. Even after Franco had gone the killing went on. Tremlett claims that in the five years after the General died, more than a hundred demonstrators, left-wing activists, students and separatists were killed by the police or the far right.

The Spanish transition to democracy was not as smooth as some would have us believe.

Amazingly, a former Franco minister, Manuel Fraga, was able to remain head of the Galician government until 2005. Spain must be the only modern European democracy where such a situation could arise. Atrocities committed during both the Civil War and mass executions carried out in the Franco era were overlooked by the new authorities. This was known as the pacto del olvido – the pact of forgetting. Tremlett visits towns where action is now being taken to unearth graves and come to terms with what happened. Victims’ familes and those seeking justice are pushing for the authorities to face up to the hidden realities of Spain’s twentieth century tragedy.

Despite its Catholic history, Spain is country where many take pride in its newfound secular modernity. Pretty much anything goes now where sex is concerned. There are reports of young men being dropped off to enjoy a drink at a local brothel by their girlfriends, a football club being saved thanks to a brothel’s sponsorship and in some sex parlours everything has been thought of right down to facilties for the disabled. A bikini may have been deemed to be indecent on a cinema screen before 1964 but some swimming pools now have nudist zones.

Giles Tremlett, is the Guardian’s correspondent in Madrid and he loves facts and figures. Some of these are astonishing: Benidorm has 330 high-rises, more than any other city in Europe apart from Frankfurt, Moscow or London. The holiday town also has 38,000 hotel rooms, apparently more than anywhere else in Europe with the exception of Paris and London. And getting back to sex again the age of consent is 13.

Is Spain a nation or several nations squeezed into one state? Tremlett goes to the northern regions with their own languages and sense of national identity as he examines the background to nationalism in The Basque Country, Catalonia and Galicia. His own life experience leaves him with a balanced view on Castilian v Catalan rivalry. He has raised his family in Madrid but after spending an earlier period in Barcelona it remains his favourite city and he openly admits to being a fan of Barça. Given this information, it is perhaps a little surprising that Tremlett does not consider Catalan a very useful language. He acknowledges that he would like to return to live in Barcelona one day but sees Catalan as an obstacle, “I can think of many other, more useful, languages I would rather learn first – Arabic, Chinese, perhaps Italian. It makes a move to Barcelona about as attractive – and likely – as going to, say, Helsinki or Athens”. It seems to me that to say that other languages are more useful is somehow to miss the point. Of course Chinese or Arabic are more significant in terms of world affairs and would prove more useful in other parts of the world but knowledge of Catalan is very practical for living in Catalonia and understanding its culture. The same goes for Flemish in Flanders, Gaelic in the Outer Hebrides and so on. In fact, Catalan has more speakers than European languages such as Danish, Norwegian or Irish but maybe Tremlett believes in a hierarchy of languages where only those with the largest number of speakers are of real value.

In the chapter on Galicia, Tremlett delves into well beaten paths such as superstition, religious conservatism and emigration. However, his account is still interesting and entertaining, as the book is throughout. He acknowledges that even cautious Galicia is changing. Fraga, one of the last relics of the Franco era, has finally been pushed out of power. Meanwhile Galicia’s coastline, which has had more than its fair shair of oil spills, is the gateway for much of Europe’s cocaine trade and drug cartels.

Almost inevitably, the shadow of ETA looms large over the Basque section. The book was finished prior to the ceasefire of March 2006, which gave new hope that a peaceful solution might be negociated. Tremlett talks to a teacher who lives under constant threat of an ETA attack, and to former members of the organisation and its victims. Also featured is the unique Basque language, of which I picked up a few words when reading this book.

While down south, Tremlett refreshingly decides to give bullfighting a bodyswerve and instead goes to find out about a less well documented but equally important part of Spanish culture. The author visits some of the meanest areas of Seville in search of the soul of modern flamenco. He discovers some extraordinary events such as the penal system’s Flamenco Song Contest. Incredibly, there was a time when the winner was rewarded with early release from jail but nowadays the victorious contestant merely receives money and a recording contract. The chapter on flamenco, tinged with sadness like the music itself, proves to be one of the book’s most absorbing and enlightening sections.

Ghosts of Spain is highly recommended reading for anyone who wants to attempt the difficult task of understanding Spanish society today and the historical reasons why things are so. It is written by someone who clearly has a deep love for the country he lives in. The topics covered are so diverse that all readers are likely to learn something new and will find themselves nodding along in agreement and shaking their heads in astonishment. To understand and yet not understand. That is the paradox.

Ghosts of Spain: Travels Through a Country’s Hidden Past by Giles Tremlett is published by Faber and Faber

Stephen Porter moved to Spain in 1998, and has travelled extensively around the country. He is the author of The Iberian Horseshoe – A Journey (serialised on badosa.com)