Spaniards, he rages on, are exasperating, inconsiderate, deeply insecure, have no sense of identity because of their refusal to accept the contribution to their nationhood of Jews and Muslims down the centuries. They exploit people like himself, a freelance jobbing writer. They expect him to cross the country and address boring conferences for peanuts just because such terms are acceptable to some eminent English Hispanicist bolstered by a cushy professorial chair.
He crashes gears and hurls round corners as we skirt the Sierra Nevada to enter the Granada uplands that sprawl luxuriantly before us. He complains he's wasted hundreds of hours correcting a botched Spanish translation of his biography of Lorca - and I'm wilting under the onslaught. "I'm the only one of a generation of eminent British Hispanicists who has actually settled in Spain. It's all right for them," he snorts, "swanning over from England to grant an interview with El Pais, but I live here."
And that's the point. Behind the diatribe, Ian Gibson, 58, adores Spain, with such an intensity that, in 1984, he took Spanish nationality. The love affair began in the mid-Sixties when he uncovered the truth about Lorca's murder in 1936 by Franco's troops.
Gibson's book, The Death of Lorca, making explicit the poet's homosexuality, was banned by Franco when it appeared in 1971, but became a classic and inspired a film starring Andy Garcia. The book will be reissued shortly to mark the film's British and US premiere, and next year's centenary of Lorca's birth.
While investigating Lorca - "Fred", he calls him - Gibson became fascinated by the surrealist master, Salvador Dali, whose biography has taken him five years to complete. "Lorca was in love with Dali," he says. "Dali summoned me in 1986 to tell me about it, when he was suffering from Parkinson's disease and his head all cluttered up with tubes. He confirmed that Lorca was passionately attracted to him and wanted to make love to him physically, but Dali was too frightened to give himself."
We reach the house Gibson and his wife Carole built some five years ago amid olive and almond trees overlooking a village of breathtaking prettiness. His rage subsides, but his verbal energy roars on. "Dali was jealous of Lorca because Lorca was dazzling in company and Dali was painfully, morbidly shy and couldn't compete. He was driven by a sense of shame and feelings of inferiority, and his lifelong need to overcome them."
Hence the biography's title, The Shameful Life of Salvador Dali, rather than the more obvious "The Great Masturbator" - one of Dali's greatest works and a description of his dominant characteristic. "The point is to explain why Dali was so fucked-up sexually, to find out what's under the surface. Dali was terrified of his sexuality, terrified of being impotent, terrified he might be homosexual. I wanted to get to the bedrock of why, so I conceived his life story as being set within a theory of shame."
He thinks Dali is the only Spaniard who has talked about masturbation as his principle sexual outlet, who gloried in impotence as the source of sensational achievements. "It was all a struggle against his pathological insecurity and shyness. Shame is the great unknown human emotion, it's about hiding, blushing, scurrying away. Dali used to orchestrate mass orgies and watch them unseen, wanking in a corner. His paintings are full of people hiding their faces, of flaccid forms supported by crutches."
Gibson found evidence in Dali's diaries - written in Catalan when he was only 17 - that the artist had fabricated his entire persona. "He admitted he was a fake, that every gesture was calculated for effect, that life was a farce and that he had to pretend to be what he was not. He swore that if he played at being a genius, he would become one."
Hence the tragedy of Dali's old age, when the mask fell away leaving a broken figure, catatonic with fear. "Once he had constructed the mask, he couldn't take it off. He worked so hard to perfect his persona he just couldn't abandon it."
Two BBC documentaries on Dali, presented by Gibson, are to coincide with his book's publication. The pathetic images they show of the artist's last years almost prompt sympathy for a personality that otherwise appears loathsome. "Making the films was a great help in finishing the book," he says. "Not least in supplying the money to keep me going."
We are lolling by the Gibsons' vast swimming pool, built with the proceeds of selling all his books and documents on Lorca to a study centre in the poet's birthplace nearby. "You don't think it's ostentatious?" he asks anxiously. I concede it is generously proportioned, but appropriately austere for a television-free household that subsists on the Guardian weekly, El Pais, and the London Review of Books. He laughs and threatens to add dolphins and fountains. "I sold my archive to get all those Lorca years out of my system."
But, unlike Lorca, whom Gibson grew to love, Dali is, he finds, impossible to love. "He was so cruel, heartless and corrupt, immersed in his sleazy world, surrounded by crooks." After his creative period in the 1920s and 1930s, Dali became repetitive, Gibson reckons, his best images - such as the melting watch - overworked and debased.
As a sickle moon rises over the terrace, Gibson sloshes Jameson into Waterford crystal tumblers he bought with the proceeds of a 1995 television series on the Irish famine. "I was a southern Irish Protestant, destined to be a Methodist preacher, but I was a good rugby player and it was impossible to play without drinking. Guinness liberated me. I owe everything to alcohol." He laughs with the easy freedom of a person who, complaints notwithstanding, is happy with his life.
Was he tempted to write about Luis Bunuel, the surrealist film-maker whose life was bound up with both Lorca and Dali? The question prompts a reprise of the rant. "I'm not going to sweat my balls off writing biographies without institutional support. I don't want to be a poor biographer for ever. I want the recognition, I'm not ashamed to admit it. Let's hope Dali does the trick"
`The Shameful Life of Salvador Dali', by Ian Gibson, is published by Faber and Faber on 3 November