The Herald Magazine cover story: Richard E Grant

On further inquiry, it turns out that pop singer Ariana Grande - "the new Mariah" says one of the devoted - is the real draw. It is an impressive turnout for young Grande, but if the fans of Bruce Robinson's 1986 comedy did not have mortgages to feed, the crowd would be enough to stop the traffic.

In the way of classics, the cult movie equivalent of Catcher In The Rye has not moved on, but its stars and director have. Paul McGann ("I") went to television, Robinson to The Rum Diary with Johnny Depp, and Grant to - well, where to start? The celebrated diaries? The films with Altman, Scorsese and Coppola? The appearance on Rab C Nesbitt? Doctor Who? And, most surreally of all, BBC One's Watchdog?

Dom Hemingway, Grant's latest movie, would be the natural starting point seeing as that is the reason we are here today. Written and directed by Richard Shepard, the comedy drama stars Jude Law as the eponymous anti-hero, a safecracker just out of prison after a long stretch. Waiting for Dom is his pal Dickie, played by Grant. While it is an all-you-can-eat buffet of a part for Law, who is rarely off the screen, Grant serves up the most piquant dishes as Dom's long-suffering consigliere. To use one of Grant's favourite phrases, he "licks the plate clean", relishing every minute.

He gives the same impression while publicising the film, which is not always the case with junkets, he admits. He should know, having plucked a couple of turkeys from the film bag in his career, chief among them Bruce Willis's Hudson Hawk. "It does make a difference if people love the movie," he says. "The amount of times I've been on junkets where people are going [he adopts a rictus grin], 'We had a lovely time, we're a happy family and it's a wonderful film.' You know you're lying and they [the press] know you're lying, and they're pretending they liked it and it's terrible. It's like going on a date where you know in advance that you do not want to be with that person, and that person doesn't want to be with you."

This is said in a tearing rush, with not a moment to lose fervour. It is an attitude the 56-year-old has learned to take with life. Born in May 1957, in the then British colony of Swaziland, the young Grant did not want for material things. His father was a director of education, his mother was a secretary, and all their set spoke with a regulation posh "wah-wah" accent. There was sadness, however. Aged 10, Grant witnessed his mother's adultery when he was in the back seat of the car, meant to be sleeping, and she was in the front with her lover. His mother left the house; his father remarried but sank into alcoholism.

Grant has explored these years in his diaries, With Nails and The Wah-Wah Diaries, and a 2005 drama, Wah-Wah, which he wrote and directed. He ticks some of the boxes for an adult child of an alcoholic, as identified by the American psychologist Dr Janet Woititz, but leaves others defiantly blank. In the latter category, for example, he certainly has no difficulty having fun. Time in his company and that of his diaries shows that. Forming intimate relationships holds no terror either, as evidenced by his immediate family: his Scots wife Joan, to whom he has been married for 27 years, his daughter Olivia and stepson Tom.

He had no difficulty understanding the friendship between the loud, boorish Dom and the gentle Dickie. "I've been in that situation where somebody's said this person that you are friends with is being a complete twat, they've done this, they've done that," he says. "You go yes, but that is what my understanding of friendship is, you absolutely recognise the faults of somebody as they do yours, but the love for each other overrides all of that."

While a long-time friend of Peter Capaldi, his closest pal in the business remains Robinson, who gave him his big break in Withnail & I. That's "big" as in Everest, Empire State Building and UK national debt. As he writes in With Nails, the tale of two penniless actors who decamp from London to the Lake District won him almost every major part on his CV thereafter. It opened doors with Robert Altman (Grant starred in Pret A Porter, The Player and Gosford Park), Francis Ford Coppola (Dracula) and Martin Scorsese (The Age Of Innocence), and it was the ultimate Hollywood conversation starter, as when Spielberg said to Grant: "You're Withnail, right?"

Robinson, who also cast him in How To Get Ahead In Advertising, makes him laugh "almost more than anybody I can think of". The two insult each other mercilessly when they meet. "You can only properly insult in a very British way somebody you trust and like." His appreciation of a first-class slagging is one of the many links he has to Scotland. Besides marriage to Joan - the daughter of a doctor from Aberdeen - and friendship with Capaldi, Grant starred in an episode of Rab C Nesbitt as Chingford Steel, a pukka Minister for Work who goes to Govan to mend "Broken Britain" and ends up being held hostage by Mary and Rab.

"Elaine C Smith," he roars, unleashing his inner luvvie. "Oh my God, I just adore her. And Gregor Fisher. Honestly, to get the call to go and be in it. I had worshipped that programme, watched every episode. My wife kept saying to me: 'How do you understand what they are saying?'"

He met Joan Washington, a voice coach who has worked on films such as Green Zone to Yentl, when she was teaching a British accents course. Grant had been told by his agent that being over six foot, with dark hair and blue eyes, he could go for Irish parts in the many dramas about Northern Ireland then being made. "I never got a part as an Irishman but I fell in love and got married." Having trained at the Central School of Speech and Drama, Washington had to go with the then fashionable flow and adopt a neutral accent. "When she gets tired, or she gets emotional, her Scottish comes walloping out."

Withnail and Advertising were the open sesame to Hollywood. His first major movies post-Advertising were the action fantasy Warlock, Henry And June, a biopic of Anais Nin and Henry Miller, and LA Story, directed by Steve Martin. Grant kept diaries throughout, covering those films plus Hudson Hawk, The Player, Dracula, The Age Of Innocence and Pret A Porter. With Nails ought to be essential reading for every aspiring actor, just as the Wah-Wah Diaries should be the first buy of any aspiring indie filmmaker. In both he is remarkably candid, especially about Hollywood, which is usually quick to tell people who step out of line that they will never work there again.

Grant says he did not censor himself, leaving any cuts to the editors and lawyers. He started keeping a diary as a form of therapy after his mother left. What she had done was so hard to take in, he says, that he instinctively wrote about it just to convince himself that it had happened. Candid as the diaries are, there is one major omission. Reading them, I had thought Grant was an only child. I later discovered he has a brother, Stuart. The two are oil and water. After Wah-Wah opened the Edinburgh International Film Festival in 2005, Stuart appeared in the papers to denounce his brother as "a poseur". Recalling their childhood, Stuart said: "We fought about everything. From who would sit in the front car seat, to me calling him a pansy."

Grant has not seen his brother in 32 years. I ask him about Stuart's absence from the diaries. "We never had a relationship that was a good one that then went south, it was just we never ever within my memory got on or had anything in common. There was nothing to write about if you like." Instead, his search for a family led him to acting.

Another defining characteristic of adult children of alcoholics is that they crave approval. This would appear to make acting, with its pendular swing between adulation and rejection, at once the best and worst career choice. It seemed like the latter in the early days for Richard E Grant (the E doesn't stand for anything, it was an Equity name clash thing, though his original surname was Esterhuysen). He emigrated to London in 1982 with a degree in drama from Cape Town University. A long spell of waiting jobs, rep and the Fringe followed. By the time he auditioned for Withnail his yearning for "the break" was almost painful. "To be (wanted), or not to be, that is (always) the question," he confided to his diary. "It's enough to make you heave but the day they do, never ceases to shift some sherbet down my spine."

Grant seems to relish feeling the fear but going forth anyway. How else would one explain that having spent his childhood trying to hide his father's alcoholism and his mother's adultery he publishes diaries referring to them and makes a film? The latter is astonishing, covering as it does the night Grant's father fired a gun at his son's head. Grant had poured his dad's whisky down the drain to stop him drinking. His enraged father chased after him with a gun and Grant dared him to"get it all over with". Dad fired, missed, pointed the pistol at himself then fell to the ground sobbing.

Grant acknowledges the diaries were a form of therapy, and he had a brief spell of analysis in his forties. In Grant's case it has always been a case of actor heal thyself. Part of that healing is acknowledging how his childhood still affects him. He cannot deal, for example, with verbal aggression. "It is too reminiscent of my childhood when my father was drunk."

As it turned out, somebody up there liked Grant as far as drink was concerned. The son and grandson of alcoholics is allergic to alcohol. At first he thought it was psychosomatic, but tests confirmed he did not have the enzyme to process the stuff. He cannot stomach it. Unsurprisingly, he has never felt this to be a loss.

There have been three families in Grant's life: the first was his family in Swaziland, the second acting and the third, the one dearest to him, is his wife and children. He has described them as "my stays, my compass, my east, west, north and south, my everything worth living and loving for". His devotion even stretches to becoming a consumer champion on Watchdog. The latter followed a call from his 24-year-old daughter, who was in her Mini Cooper, driving along a motorway, and the steering locked. Grant was in Miami filming when he heard. "I felt as if I had been punched in the heart."

Horrified, Dad got on the case. Told they would have to pay to have the problem fixed, he took to Twitter, unleashing a tirade against Mini. "Clenched fists & bared gnashers set to Grrrrrrrrr!" was one of the tweets. The company did the repair for free as a gesture of goodwill. He could have left it at that, but having been contacted by other drivers with similar complaints, he went on Watchdog in September this year.

Soon he will leave the hotel, past all those Ariana Grande fans, for another junket gig. "You're going back to Scotland, aren't you?" he asks. No, I say. I'm in temporary exile for the London Film Festival and missing home already. "You're like Muriel Gray!" he shouts. The two had been hosts at an event a few nights before for Mothers2Mothers, a charity working to prevent transmission of HIV from mother to child in sub-Saharan Africa. Though the night finished at 1am, Gray was planning to be up again at dawn to return to Scotland. "The pull of Glasgow is obviously magical," he laughs.

As far as where he is going in his career, he would love to work with Robinson again, "a great big political rant" that he could do in the theatre. Of all the directors he has worked with, aside from Robinson, Altman affected him most. "Even though he was as old as my father he was the most genuinely young-at-heart, free-spirited puppet master of a director that you could wish for."

He has just wrapped on Queen And Country, John Boorman's sequel to Hope And Glory, and he has not given up on the idea of directing his own film again. Two projects were ready to go, only for the funding to collapse weeks before shooting. "I will try again," he says. One hopes so, because he has plenty more to contribute as a writer, director, actor and diarist. For Richard E Grant as much as for Ariana Grande, blank pages await. n

Dom Hemingway (15) opens on Friday.