During the Spanish civil war the single greatest atrocity perpetrated by the Republicans was known as ‘Paracuellos’. This was the village where an estimated 2,500 prisoners loyal to Franco were executed by leftish militiamen between November and December 1936.

Even though the facts of this massacre are now widely known, one question still remains: who ordered the killings? In his latest book The Last Stalinist,Paul Preston claims that it was Santiago Carrillo who played a crucial role in signing the death warrants. (Carrillo, who died in 2012, always denied any involvement in the incident).

It is worth mentioning this mass murder because history tends to catch up with power-hungry leaders devoid of moral integrity. With Carrillo, however, this hasn’t been the case. It is even proposed that a street in Madrid be named after him, for his contribution to the restoration of democracy in Spain.

Santiago Carrillo was the leader of the Spanish Communist Party (Partido Comunista de España) for two decades, and his politics — with a penchant for authoritarianism, doublespeak, supreme self-confidence, irresponsibility and Soviet-style interrogation methods — was driven by an unquenchable thirst for power. And while he may have always been the number one enemy of Spain’s far right, he shared with Franco, according to Preston, ‘a dedication to the constant rewriting and improving of his own life story’.

He was born on 18 January 1915 to a working-class family in Gijón in northern Spain. From his early teens he was steeped in the radical-socialist politics of his father, Wenceslao Carrillo, secretary of the Asturian metalworkers’ union. During these years he learnt a valuable lesson about politics while observing his elders — namely that the organisational structure of how a party works actually matters more than polemics.

In October 1934, as Fascism loomed ever closer, Carrillo was arrested for attempting to stir up socialist revolution and sentenced to 17 months in prison. On his release in February 1936, he was invited to visit the Soviet Union, during which time he became a committed communist and puppet of Moscow. When Stalin commanded, Carrillo obeyed — seeming entirely comfortable in this submissive role— and with his incorporation into the Politburo, his transformation into a hardline Stalinist was complete. In 1939, while living in exile in France at the end of the civil war, he even wrote an open letter denouncing his own father for joining the junta set up by Colonel Segismundo Casado to negotiate with Franco.

Anyone who questioned Carrillo’s authority within the PCE was threatened with retribution. One such victim was Pascual Gimeno Rufino, whose body was found in July 1945 near a railway station in Valencia. Preston explains that he was murdered on Carrillo’s direct orders, because an internal Party investigation suspected that he had become a police informant.

During the 1960s and 1970s, Carrillo began a process of modernisation in the PCE. All far-left hardliners were expelled, enabling him to maintain a firm grip on power as politics inevitably moved to the centre with the ending of the Franco era. While his political views may have been inconsistent, Carrillo always preferred conformity over ideology, to better his chances of personal advancement through the PCE hierarchy.

Preston’s sympathies lie very markedly with those who fought with the Republicans, and this book aims to uncover what he sees as the great betrayal of the thousands of militants who suffered in the struggle against Franco. He suggests that an intellectually curious leader might have presented a more formidable opposition than Carrillo ever did to the ruthless dictator’s regime.

The investigative edge to Preston’s analysis, backed by countless documents and decades’ worth of interviews and sound historical research makes this biography an enormously engaging and authoritative source. I must admit, however, that some of the information — though fascinating — I found difficult to digest, given the book’s extremely long and detailed chapters; and the author certainly assumes much prior knowledge of Spanish history and politics on the reader’spart.

But these are minor cavils, and The Last Stalinist is yet another reminder that Paul Preston remains the most reliable historian in the English-speaking world for anyone wishing to understand the complicated power struggles between left and right in Spanish politics over the course of the 20th century.