Adrian Newey is described so routinely as "a genius" that his more evocative journey, as the most successful design engineer in Formula One, is often forgotten. The revered maverick, who always uses a 2B pencil rather than a computer to create his dazzling cars, has won an imposing 119 races, seven constructors' titles and six drivers' championships. But, in person, Newey emerges as an engaging man who readily confronts the tangled emotions that have punctuated an otherwise brilliant career.

Newey might be able to laugh at the fact that he was expelled from school, and fired from his first job in Formula One, but he felt real distress 17 years ago this month. Ayrton Senna died in a car Newey had designed – and the engineer was charged with manslaughter. That bleak period provides an enduring if haunting perspective from which to consider Newey's latest triumphs.

"In many ways," he says, "winning the constructors' and the drivers' titles with Red Bull last year was the most satisfying of all. When I left McLaren to come here in 2006 lots of people said: 'Newey's bitten off too much this time. He's going to fall on his face and wreck his career.' I try not to be affected by what other people say but everything we've achieved over the last five years has been amazing."

This season, with the fifth grand prix of the year due at Barcelona on Sunday, Red Bull are already 43 points ahead of McLaren and Sebastian Vettel is 34 points clear of Lewis Hamilton.

"This has always been the aspiration," Newey says of such domination. "But I totally underestimated the task of building a new team. Initially I tried to keep my work design-based, but it quickly became apparent that we didn't have the facilities for that. I started to concentrate on building an infrastructure because, without it, we couldn't develop the car. I found that interesting and, I guess, there was a sense of unfinished business."

In 1990, Newey had been sacked by a struggling March team. "There was quite a lot of self-doubt. We'd had some success with the 1988 March car but I was 28 and somewhat naive. We were over-ambitious and I went from the hero to a guy who didn't know what he was doing. I was fired but I'd already made up my mind I was going – because once a team gets run by an accountant, it's time to move. Your self-confidence does suffer but Williams had approached me."

Nigel Mansell, Alain Prost and Damon Hill all won the world title in cars Newey designed for Williams; but his memories are clouded by Senna's tragic fate with the team. A brief partnership between, arguably, Formula One's greatest racer and designer ended in the death of Senna as he inexplicably left the track at high speed while leading the 1994 San Marino Grand Prix.

Newey shudders when asked how Senna's death affected him. "Well," he says after a poignant hesitation, "the little hair I had all fell out in the aftermath. So it changed me physically. It was dreadful. Both Patrick Head [the Williams technical director] and myself separately asked ourselves whether we wanted to continue in racing. Did we want to be involved in a sport where people can die in something we've created? Secondly, was the accident caused by something that broke through poor or negligent design? And then the court case started."

Head and Newey were both charged with manslaughter. "The court case was a depressing annoyance, and extra pressure, but it did not make me question whether I wanted to be involved in F1. It's the self-searching rather than the accusations that really matter."

Was Newey close to abandoning racing? "Yes," he says quietly. "For the whole team it was incredibly difficult. I remember the day after the race was a bank holiday Monday and some of us came in to try and trawl though the data and work out what happened. They were dark weeks."

Head, as the technical director, was controversially found guilty of manslaughter in 2007. But he was never arrested as the statute of limitation under Italian law had passed the designated term. When did Newey finally absolve himself of culpability?

"The honest truth is that no one will ever know exactly what happened. There's no doubt that the steering column failed and the big question was whether it failed in the accident or did it cause the accident? It had fatigue cracks in it and it would have failed at some point. There is no question that its design was very poor. However, all the evidence suggests the car did not go off the track as a result of steering column failure."

Calmly, even if his face creases with the painstaking detail, Newey steers me through the possible causes of the crash. Ultimately, after an almost forensic analysis, he concludes that the rear of the car "stepped out" because, "the right rear tyre probably picked up a puncture from debris on the track. If I was pushed into picking out a single most likely cause, that would be it."

Newey shakes his head when asked if he has seen the recent and riveting film: Senna. "No. It would not be an easy thing to do."

He also thinks carefully when asked if Vettel might one day warrant comparison with Senna. "I always find that difficult to answer. The truly great drivers I've worked with have all been very determined. They all have great self-belief. But they work hard at it. Sebastian will often work late trying to understand how the car is working and how he can improve. He's a quick learner and rarely makes the same mistake twice.

"At the moment he's really on top of his game. So far the gap between Sebastian and Mark [Webber] has been bigger than last year. It's certainly not a case that Mark has been driving any slower – that's for sure. Mark's just taken a bit longer to adapt to the Pirelli tyres but the gap is closing."

Newey waves away the latest inflammatory suggestion made by Helmut Marko, Red Bull's racing consultant, that Vettel and Hamilton would make a "fantasy" pairing.

"Crikey," Newey snorts. "I'm hoping Mark continues next season. Apart from being a great person, his contribution has been significant. He's been a pillar of the team from the start. Seb is very perceptive in his feedback in some regards and Mark is very perceptive in other areas. We listen to both and it helps the car."

The tension was marked last year, with Vettel and Webber scrapping for the title and almost allowing Fernando Alonso to sneak past. "It was one of the hardest championship-winning seasons for many reasons," Newey says. "Collectively we made hard work of winning it even though we had the quickest car. We threw huge amounts of points away and had growing friction between Mark and Seb."

Newey smiles as he looks at me. "Your colleagues are very good at winding up both sides, because this sells a story. Unfortunately both drivers were influenced by the press and were a little naive – because you shouldn't take heed of that. And then we had constant sniping over the legality of our cars."

Red Bull's design was cleared after a very thorough investigation. This year the carping has been muted. But Hamilton has voiced concern that Red Bull's front wing might be fractionally lower than regulations allow. "It gets boring," Newey shrugs. "When one team snipes at another about the legality of its car it can be out of simple jealousy or because the griping driver is being fed by his team who are telling him his rival's modification might get banned. When a driver starts griping about a competitor's car it's clearly coming from the team. Drivers don't suddenly become experts in front wings."

Newey understands the tendency of writers to become romantic about the fact that he uses a pencil rather a computer to create his racing masterpieces. In his office outside Milton Keynes, Newey spins round in his chair and looks rather lovingly at the drawing board he has used since he was with McLaren – where he designed cars which won successive world championships for Mika Häkkinen in 1998 and 1999.

"I've won three drivers' and two constructors' titles with it," he says fondly. "I'll often start with a sketch on a piece of A4. Then I'll develop that on the drawing board – using freehand sketching. That's something you cannot do on a computer and it feels very natural."

Newey seems more amused than flattered by the "genius" word. "Coming up with ideas is interesting and indefinable, isn't it? The brain is a funny thing. An idea often emerges in the shower, or during a walk. Your brain has been ticking away and the idea just bubbles up. Occasionally you feel, 'God, I've gone dry.' It's like writers' block. Shortly before the launch of a new car, when I've used all my existing ideas, I think, 'Now what?' But running the car produces new ideas as you understand what you've created."

Ferrari would love to lure Newey away – and he confirms that last year he rejected their latest approach. "They're a great team and just like many drivers end up succumbing to Ferrari's romance, engineers aren't completely callous. But I won't be going to Ferrari. One reason is that my family [with four children] is in England. And being involved with Red Bull from the start has been hugely rewarding. I have no desire to work for anyone else in F1."

Newey was expelled from public school when he organised a pop concert which blew out some prized stained-glass windows – and he only made it to university when, after missing his A levels, he obtained an OND in engineering. He laughs at being tempted by a friend's suggestion that he might eventually move out of Formula One and into academia: "Maybe in years to come I'll don a smoking jacket and Hush Puppies."

He scratches his head at a reminder that he has always said he will retire from racing before he reaches his 60s. "They're creeping up," he says. "How old am I now – 52? 53?"

The genius looks bemused by a taxing question. "I'm 52, I think. Yes, it is 52."

Newey is too consumed by work to be bothered with such trifles. "I love the variety and the blend of creativity and competition. The downside is that you're under constant pressure. But you constantly see the rewards of your work. When it's not going well it's salutary and perhaps then you'd rather be working for British Aerospace. But when you're really flying it's just a great feeling."