The surviving family can be very protective of the reputation of a well-known predecessor. Esteban Volkov, grandson of Leon Trotsky, has more reason than most such descendants to defend his famous forebear. After Lenin, Trotsky was the most important leader of the Bolshevik revolution in 1917, but, vigorously opposed to Stalin's bureaucratic dictatorship, he was expelled from the Soviet Union in 1929, constantly vilified and finally assassinated in 1940.  I met Volkov in the same Mexico City house he shared all those years ago, as an adolescent, with his grandfather, his grandfather's second wife Natalia, plus a number of bodyguards and secretaries. The same home from which Trotsky kept up his ceaseless struggle against Stalin. To preserve his grandfather's memory, he has since turned the house into the Leon Trotsky museum.  Volkov is now in his mid-70s, slim and very fit looking. A retired chemist, he is widowed, with four daughters and five grandchildren. He is at first reserved, and speaks his Mexican Spanish with a slight accent which hints at a family history out of the ordinary. "I am the only person in my family to reach my age," he says, with a grim smile.  Stalin was responsible for the death of practically all of Trotsky's family, whatever their political stance. We total up the closest relatives - Trotsky's first wife, his sister, his brother, one son, two son-in-laws and three nephews were all arrested and later shot; another son was assassinated. His two daughters were harried to their deaths. Others disappeared without trace.  Among the deaths were Volkov's parents. His father, Platon Volkov, an oppositionist, had been deported to the gulag, and shot at some unknown date in the 30s. His mother, Zinaida, left the Soviet Union with Volkov when he was five: he did not know until much later, in 1988, that his half-sister who they had left behind had survived - his mother had only been allowed to take one child with her. Volkov believes the consequent torment she felt was one of several such factors that pushed her to suicide two years later, in 1933.  Wasn't fear a permanent factor during his early life? "The time I remember really feeling afraid was in Paris," he says. By then an orphan, he was staying with his Uncle Lyova, Trotsky's son, and his partner. "Sometimes, when I was alone in our flat, I had the sensation of someone trying the lock to get in." Documents made available 10 years ago revealed that agents from the Russian police, the NKVD, were staying in the flat next door.  Soon enough, Lyova was also murdered by Stalin's men. Trotsky initiated a court case in Paris to gain custody of young Volkov from his uncle's surviving partner. She refused to abide by the judge's ruling and went into hiding with him, but friends of Trotsky found him and brought him to Mexico - for which Volkov remains grateful.  So it was that in 1939, as a 13-year-old, Volkov came to Mexico to rejoin his grandfather. It was a difficult and confusing time, not only emotionally but linguistically. It was already his sixth country, following Russia, Turkey (where he had spent two years with Trotsky), Germany, Austria and France, and Spanish was the fifth language he had to deal with. "I had forgotten my Russian, so I had to speak French to Trotsky and Natalia. Spanish is now my native language," he adds with a touch of pride. Also in Mexico he became "Esteban", the Spanish equivalent of his Russian first name, Vsevolod, or Seva for short.  It might seem strange that someone of Trotsky's stature will now be better known to many as a footnote in the life of Mexican artist Frida Kahlo, thanks to the new biopic, Frida, which has its London premiere this evening. In it Trotsky (played By Geoffrey Rush) is shown, newly arrived in Mexico with his wife, becoming the lover of Frida (Salma Hayek) - in what can safely be assumed is the only Trotsky sex scene ever filmed.  Volkov is sceptical about the affair. One of Trotsky's Mexican bodyguards once told him that, because of the constant presence of those protecting him, "Trotsky was never alone long enough to conduct an affair without it being known". Not that he is overly concerned to protect the image of his grandfather in this particular area: "Trotsky was after all a man, and could easily have been caught in Frida's net." She was much younger "and had many lovers, women as well as men". Volkov got to know her and her circle very well, starting in the mid-1940s, about five years after his grandfather's death. "She was a really wonderfully warm and remarkable personality. I liked her a lot."  Whatever had really happened between her and Trotsky, there is no doubt that afterwards Trotsky still maintained excellent relations with Frida's husband, the renowned leftwing muralist Diego Rivera, who had successfully lobbied to win asylum for Trotsky in Mexico. When the two men did finally fall out it was because of political differences, Volkov insists. Trotsky and Natalia moved out of "the Blue House" (now the Frida Kahlo museum) where they had stayed as guests of Frida and Rivera and moved two blocks north and three blocks east across Coyoacan, a lovely district then just outside Mexico City.  However, Volkov recalls, Trotsky could not risk strolling around the tranquil tree-lined streets for fear of an assassin's bullet from an NKVD agent. "When he left the house he always went in a car, with another behind or in front with more bodyguards," says his grandson.  The risk of leaving what Trotsky called his "prison" meant curtailing his much-loved visits to the Mexican countryside to collect cactuses. But one regular activity the Soviet exile enjoyed without having to leave the protection of the 20ft garden walls, says Volkov, "was to look after the rabbits kept there which were eaten and the chickens which provided fresh eggs".  But however cautious he was, Trotsky and those around him were in danger from Stalin's agents. In May 1940, a year after young Volkov's arrival in Mexico, there was a massive nighttime assault on the house. Volkov attributes his survival to a rapid decision to dive under the bed. A large group of Mexican communists, under orders from Moscow and led by the artist David Siqueiros, fired their Thompson machine guns into his bedroom and that of Trotsky and Natalia. All three miraculously survived, with only Volkov slightly hurt in the foot. For the moment there was elation fed by relief, but for the 60-year old revolutionary it was a reprieve of just three months.  In August, Ramon Mercader, an NKVD agent of Spanish origin, murdered the "Old Man", as he was known in the embattled household. The killer used an ice pick, striking Trotsky's head while he sat at his desk, reading an article about which Mercader pretended to want his opinion.  "I was coming home from school," Volkov recalls. "Approaching the house, I was seized by a feeling of anguish as soon as I saw that in front of the entrance were unusual movements, and cars parked in a hurry. I quickened my step, and then I saw the shocked faces."  Entering, he saw police officers in the middle of the garden holding Mercader. Volkov knew the assassin: he had formed a relationship with one of Trotsky's secretaries to gain entry to the household. "He was dishevelled, his face unrecognisable; a man disfigured, groaning and sobbing." Mercader had been attacked by Trotsky's guards, who rushed to the scene after hearing his scream.  "I had no idea what was happening," says Volkov. "When I went into the study, I saw Lev Davidovich [Trotsky] wounded, lying on the ground, but the guards and others stopped me from going any closer. My grandfather had said: 'Don't let Seva in, the child mustn't see this.' Later, he crossed the garden for the last time, on a stretcher carried by male nurses." He died the next day in hospital.  Volkov maintains that even as a child and adolescent, he had a clear if rudimentary awareness that Stalin was "a bloody dictator responsible for the death of millions, who had betrayed the revolution, and that Trotsky reminded the world of this fact. This is what made him afraid of my grandfather." It also made Trotsky's death an obsession for Stalin.  After the traumas of his early years, Volkov led a relatively normal life with a family; a middle-class professional doing interesting work synthesing hormones in the pharmaceutical industry. He has stayed unswervingly faithful to the memory of his grandfather. This has not taken the form of political activity, but through the museum - which Geoffrey Rush visited while researching his role in Frida. Like the other 24,000 visitors a year, the actor entered Trotsky's austere old home, saw the bullet holes from the failed assassination attempt, and the study where he was murdered. It provides a chilling reminder of how Stalin used his power to crush any opposition. An exhibition of photos and captions plus a modest collection of documents and artefacts tell the story of Trotsky's life, his family, his struggles and his murder.  He argues that Trotsky's real legacy is "of a genuine socialism which is democratic, which still needs to be on the political agenda.  "The more grotesque lies about Trotsky have disappeared with the regime that manufactured them," he says. "But there still exists another distortion, the one that equates Trotsky and Stalin as two bad Russian bears," - the only real difference being that Stalin won. "But it went deeper than a personal power struggle. It was a conflict over what type of society the Soviet Union should be," he says, leaning forward and becoming much more animated.  "Stalin was the builder of a bloody, oppressive and bureaucratic system. Trotsky led and defended a revolution. There is no comparison."  · The Trotsky Museum, Av. Churubusco 410, Coyoacan, Mexico City. mx.geocities.com/museotrotsky. The British premiere of Frida is at the Odeon Leicester Square tonight.
Esteban Volkov tells Phillip Hall about life with his grandfather, Leon Trotsky, how he survived Stalin's slaughter of his family, and why the new movie, Frida, has got it wrong about Trotsky and Frida Kahlo