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So Ron Dennis does have a sense of humour. Maybe I should have paid more attention to the little quip he made to certain journalists on Saturday morning, at the end of the second session. "There are advantages in showing your hand at the last minute... but there are disadvantages, too."

You've got it. After the brand new McLaren-Honda MP4/4 had a very promising first outing at Imola - so promising it was almost spectacular - the Marlboro McLaren team set off for Rio in haste. But in Rio it was a very different story.

Ayrton was to be responsible for the engine tests as he is particularly au fait with that side and knows the Honda V6 well. He was also due to have the spare car at his disposal and that always allows for excellent back to back comparisons.

Perhaps I should explain the role of the spare car this year. Traditionally at McLaren the spare alternates between drivers from Grand Prix to Grand Prix. This year we are doing it differently.

We tossed a coin, with the winner choosing at which event he wanted the spare. Ayrton won the first two goes and he immediately chose Rio and San Marino. I won the third and chose Mexico. In addition to Mexico, I will have the spare at my disposal in France, England, Hungary and Portugal. Senna will have it in Germany, Belgium and Italy.

At Monaco, Canada and Detroit we will probably have a spare each. But its allocation for the last three GPs of the season has yet to be finalised - it will probably go to which one of us is best placed for the championship.

So, in Rio I didn't have the spare - and my race car was definitely misbehaving. It was especially twitchy and although I had been quickest in Friday morning's untimed session I couldn't avoid a huge spin on the lap following my flier. Bang in front of the pits. Caught red-handed!

Some spectators said I appeared to lose control of the car coming out of the final bend. Others believed something must have broken. Ron Dennis opted for the first solution, but I wasn't so sure. I had tried to catch the start of the slide, but the car reacted unexpectedly.

At first sight neither the chassis nor the suspension had suffered too much from the incident. It did, however, take two long hours to get everything back into working order, which took up virtually the whole of the first timed session.

Trouble was that the spare car was set up for Ayrton, and I couldn't really use it. But, a few minutes before the end of the session, I was finally able to use my first set of qualifying tyres. My car was ready, but although thoroughly checked over, it turned out to be very unstable, especially under braking when it pulled terribly to the left.

I was fourth on the provisional grid but it wasn't a true reflection of the car's capabilities. Senna had already shown what it could do and had taken pole position.

By Saturday morning Neil Oatley, my race engineer, had discovered the cause of my spin the day before: one of the rear springs was fouling the gear-box. It was fixed and I set off again confident. The other problems had been solved, too. The gearbox that had been whistling like an old lorry? Fixed. It was a faulty second gear. My seating position? Modified.

We had, therefore, progressed well and I set off to work with 130 litres of petrol, nearly a full tank, on board. I did two laps, but quickly returned to the pits. There was a new problem. Neil, Ron Dennis, Gordon Murray and Steve Nichols all investigated the car, and noticed that the front wing was pulling away from the nose.

This suggested that the chassis might not be able to stand the pace, and this was a sufficiently serious incident to set up a huge council of war. Ayrton was stopped and all three MP4/4s were immediately put under the microscope. The atmosphere was very tense, but it soon appeared that it was a manufacturing fault confined to my car. However, all the cars were reinforced, just in case.

Given the all-clear, Ayrton continued the session and I hung about waiting for the spare to be adapted to my seat and pedal fittings. This took up the rest of the untimed session, so when the circuit opened for the final hour of qualifying I threw myself out without really taking time to adjust to the car... rain was threatening. But I knew immediately it wasn't perfect. Still, despite being down on boost, I managed to improve my best time of the day before by 3secs.

By then, Ayrton had set the pole position target at lm28.09s, I had the boost adjusted, did a few laps to check it and put on my second set of tyres. This time it just had to work.

It was even worse. I gave my absolute all and got a time of 1:28.782. The front right wheel bearing was pumping out its grease, and the undertray was starting to tear away, making for a very unstable car. A true Beresina! (Ed - Beresina: A French disaster, named after the river Napoleon expected to be frozen on his retreat from Russia. It wasn't. 12,000 died.)

What do you do in a situation like this? Not a lot; it was better to call it a day. These Brazilian Grand Prix qualifying days had been a real race within a race because so much had to be done so quickly.

Joking apart, I have found in Ayrton a team-mate with a real passion for his job, and he's probably as much of a perfectionist as I am. It's the first time in my career that I have been paired with a driver of this class, so single-minded in his desire for success in Formula 1.

We decided pretty quickly I should keep the spare for the race. Having finished the preparations I left to have dinner in a churrascaria near the hotel with my pal Stefan Johansson and a few friends, knowing that on race morning I would only have about half an hour to fine-tune the spare.

And it was raining for the warm-up! I had to make do with a few hastily made adjustments. It was at this point that I sorely missed the four test sessions that Senna had had. I just had to wait for the beginning of a race in which I was driving an unknown quantity, a McLaren whose behaviour I knew very little about. It was uncertain stuff.

The race turned out to be a completely different matter. Luck smiled on me, if one can use the word 'luck' about this business I must thank my team, which between Saturday night and Sunday morning did the impossible in making requests into reality.

The changes I had asked for gave me the opportunity to drive a Grand Prix that turned out to be a piece of cake. I was able to control the race from start to finish, helped by Ayrton's gear linkage problems and, finally, his disqualification.

Before the black flag he had come up the field sensationally, but when my pit board warned me he was in second place, 30secs behind, I speeded up to increase the gap: 31.2secs; 32.1secs; 33.8secs; before stopping two laps later to change tyres and rejoin, still in the lead. Those were the tactics.

But we weren't really in the same race. Senna had started the race from the pit lane and was two laps ahead from a fuel point of view - his car hadn't done two warm-up laps, remember.

After the Senna episode came the Berger drama. After the race my friends congratulated me, but told me off for frightening them. Yet, from where I was sitting, Berger's attack didn't impress. In the first place, I had chosen to make only one tyre stop, and so I had to overtake some backmarkers and that had made me lose time, too. And I knew exactly what the Ferrari could do.

I decided to go fishing, getting the Ferrari on the end of my line and letting it tire itself out. Then as soon as Berger closed to within 10secs - a self-imposed limit - I pushed a bit and Gerhard then backed off.

To be honest, at no point was I worried by either Senna or Berger. In fact, the only fright I had was on the starting grid when a Brazilian fan, a little more enthusiastic than the others, tried to kiss me a few seconds away from the green light! That made me jump. It wasn't the best way to concentrate on the start of the first race of the season.

Still, it must mean I'm popular in Rio - after all, I'd already had four wins there and this was to be the fifth…

Alain Prost, FIA World Champion 1985/6