Before the San Marino Grand Prix weekend of 1994, I was the “number one number two” in Formula One. I was team-mate at Williams to the already legendary Ayrton Senna.

By the Sunday night, however, the whole course of my life had been changed, not only because the fabric of the sport had been ripped apart with as much violence as the accidents that claimed two lives that weekend, but more because I have no doubt that I would never have been world champion if Ayrton had not been killed at Imola.

I have never publicly given my version of the events of that weekend, other than to give the bare technical facts to the investigators. I was there. I was intimately involved. I was deeply affected. I drove an identical car in the same race. I remember everything only too well.

The previous season I had had Ayrton’s nemesis from earlier in his career, ALain Prost, as a team-mate, so I was getting something of a unique and concentrated insight into the complex and intense relationships and personalities of Formula One’s sharp end. Add to that having been Nigel Mansell’s “monkey” understudy test driver the year before that and the picture emerges of me as an initiate on a steep learning curve. Unfortunately, it was to get a lot steeper much sooner than I would have wanted.

I was only six months younger than Ayrton (a not-so-young 33) but, in Formula One terms, I was just a boy and in only my second season. He, by comparison, virtually was Formula One. The previous season he had held Formula One in contempt by not deciding if he would turn up to the races until 24 hours before the event. This, understandably, made him somewhat controversial and, in certain circles, unpopular. But his maverick streak was as revenue-generating as it was petulant and he could drive like a god.

Indeed, it was to God that he ascribed his genius and he had developed an almost messianic character. Ayrton publicly talked about his Christian faith and that he studied the Bible, and he suggested from time to time that he felt divinely guided. The outpouring of grief, especially in Brazil, was somewhat more than one would ordinarily expect from the death of a sports star, and the evidence was that Ayrton had some “ other power” that people recognised in him. The manner in which he went about his work reflected the absolute seriousness with which he regarded what he was doing, something I was watching intently, learning for all I was worth.

The 1994 season had jolted into action with Ayrton in a new team, Williams, and a young whippersnapper from Germany called Michael Schumacher humiliating him in his own country. Michael won the first two races of the season, with no finishes for Senna. I was actually ahead of my team-mate in the championship going into Imola.

But all was not good. The Williams was not responding well to the new regulations that had forced a return to the less complex type of suspension, from computer-controlled “active” to traditional “passive”. In addition, Senna was still trying to settle into his new environment at Williams, having been at McLaren for the previous six years. The new car was not to his (or my) liking. We had yet to find a good set-up: that is to say, to drive it really fast was really difficult. We both had to push ourselves to our limits and beyond to extract what the car was capable of. So there was work still to do to get the best out of the FW16 and there were the expected “new car” problems. The car was typically cramped as the chief designer, Adrian Newey, had whittled away every spare gap to enhance its aerodynamic efficiency.

Ayrton had wanted some modifications made before the start of the season to create more room for him to work. The steering column was made thinner to enable the steering wheel to be raised and the monocoque was cut away to create more clearance for the knuckles. My car, too, was changed in exactly the same way. Much controversy was raised about these details in the weeks and years after his crash, but I will explain later in the series why I believe this to be a red herring.

There was also an uncomfortable feeling that new rivals Benetton were up to something unfathomable. They certainly had a distinct advantage when it came to employing the fuel-stop strategy necessary for ’94. This factor was one of the many possible influences on the mind of Ayrton during the race. It was now possible that the car behind was not on the same level of fuel and, therefore, deceptively faster or slower. This would have meant that Ayrton was working in the dark and would have to work harder than normal to ensure a significant gap was generated. And “harder” for him was another level altogether.

But there was more on Ayrton’s plate than we may ever know and certainly more than anyone knew at the time, even before Roland Ratzenberger’s crash on the Saturday. Recently there have been suggestions about relationship problems within the family regarding Ayrton’s new girlfriend, which I know no more about than I read. I was totally unaware of it at the time. One was aware, however, that Ayrton had more to think about than the race itself and there was an air of things getting serious from now on. The Autosport front cover for that weekend was “Can Senna take the heat?”

Traditionally, whoever won the San Marino Grand Prix usually went on to become champion, so the pressure was mounting. There was also this new chap, Schumacher, who seemed to show no respect or due regard for a three-times world champion. The tension shot up another notch in first qualifying, when Rubens Barrichello’s car was seen flying, or so it seemed, into the grandstand at the last chicane.

If it means anything to hold one’s breath for only two seconds, this was the time. How the fencing held the car, which flip-flapped along its length and finally back on to the track, is the engineering mystery of all time. How Rubens wasn’t hurt was another one. We all brushed ourselves off and carried on qualifying, reassured that our cars were tough as tanks and we could be shaken but not hurt.

The next day, that was proved unequivocally to be a myth. In a brave attempt to qualify his “back-of-the-grid-or-bust” Simtek, one of the nicest men in Formula One, Roland Ratzenberger, flew unchecked at maximum speed into the concrete wall, just one corner after Tamburello, where Ayrton was to crash the day after. His front wing had come off, possibly because of a trip over the kerbs on the previous lap. I passed by slowly as the red flags were waved to stop the session.

Roland was slumped, seemingly unconscious, in the intact ****pit. It did not look too bad at the scene… until we saw the replay. The speed of impact and the angle was sickening. The car may have withstood the forces, but poor Roland could not have. A silence fell over the circuit as we waited in case the session was restarted, not knowing the whole truth. It was only when mechanics started packing up and the TV monitor displayed “End of Session” that we knew this was bad. We all went back into the truck, as we would do normally for a debrief, but the mood was sombre.

Ayrton had gone to the scene to see for himself. Professor Sid Watkins (the head of the FIA medical commission) talked with him and I think tried to persuade him not to see, but about that I’m not sure. Whatever, when he came back to the truck he told us that Roland was dead. He was upset and angry. It was typical of Ayrton to want to know, to get involved. But what made him different from the rest was that he saw Formula One as his own domain. He regarded it as totally within his rights to go to the scene and ask those involved what had happened and what they were doing. You had the feeling, even then, that he knew he was looking, potentially, at himself.

So that made Rubens’s little dance mere entertainment: he turned up on race day with nothing more than an arm in plaster. Everyone was relieved to see him, but it was not enough to totally lift the gloom. Apparently, there was talk of Ayrton not racing, but that went over my head or around it. I had a job to do. I had my wife, Georgie, with me, so there was someone I could confide in, and Ayrton even reassured her that I was safe in a car like a Williams.

But we all knew that once you decide to be a racing driver, you have to understand that these things are bound to happen. It would be admitting that you had had no idea of the real risks to pull out now, or so the reasoning went. Now was the time to show what you were made of and be professional. Nothing less was expected, either of us, or by us. Nearly all the drivers had no question about racing the next day. But we had no idea that our puny philosophy was about to be taken to breaking point.

The mornings of a race in those days consisted of a warm-up of half an hour, in which Ayrton was quickest, quicker than me by a mind-busting second. Frank Williams could be proud of his No 1. I don’t mind admitting I had some ground to make up there, but as a team we had more hope for the race. Maybe the tide was turning.

After the warm-up we went to the drivers’ briefing. Ayrton was upbeat and determined after his good performance, but he had concerns about the new safety car regulations. These fears were to be prophetic. It was a measure of the political climate of Formula One that A. S. felt it necessary to get other drivers to ask questions about the safety car so that he did not appear to be alone. The implication was that the bosses made the rules; if you had issues with that, they would make sure you knew who ran things. So we got on to the subject of the safety car (importantly distinct from the “pace car” used to spice up US racing).

Ayrton became vociferous, claiming that it was ill- conceived and dangerous for one specific reason — the temperature of the tyres of a Formula One car is critical in several respects. One, they only stick when they are very hot; two, the pressure varies enormously with temperature and, consequently, the stability of the tyre construction.

To sum up: if a Formula One car has to follow an ordinary road car it will not travel fast enough for the tyres to keep within their designed working temperature and pressure. I believe this was a contributing factor in Ayrton’s accident, as the safety car was deployed directly after the start, exactly as he had feared.

And so it was we left the briefing on Sunday having agreed to pay some kind of tribute to Roland on the grid. We went to the normal sponsor functions and then back to the motorhome. I never really talked or spent any time with Ayrton before the race. Everything was extremely businesslike, with an added severity because of the death of Roland.”