Frank Williams, owner of the Williams Formula One racing team, yesterday denied that faulty steering played a role in the fatal crash involving Brazilian driver Ayrton Senna at the 1994 San Marino Grand Prix in Imola, Italy.

Williams was giving evidence at a trial in Imola where he and five others face manslaughter charges in relation to Senna's death. Also charged are Williams technical director Patrick Head, former team designer Adrian Newey, Roland Bruynseraede, an official from Formula One's ruling body (FOCA), and two Imola track directors, Federico Bendenelli and Giorgio Poggi. All six men deny the charges.

Since the trial opened last February, prosecuting magistrate Mauro Passarini has tried to prove that Senna's 155 mph crash at the infamous Tamburello bend was caused by the disintegration of the steering column which had been cut and re-welded at Senna's request on the day before the race.

In court yesterday, Williams rejected that view, pointing out that extensive tests, carried out by his team following Senna's death, had found nothing wrong with the steering columns on all the other Williams cars. "After a lot of examination . . . and a lot of simulations, we as a company began to formulate an opinion that the steering column did not break." Williams went on to say that, although his team had found nothing wrong with the steering columns, it was, nonetheless, decided to change the columns and make "different versions". Asked why, he replied: "To remove any doubts about the integrity of the columns." When further asked if he had made the changes because he had had doubts about the integrity of the steering column in Senna's car, Williams replied: "Absolutely. Yes, we had doubts, that's why we're here today, to try to find out what happened."

Williams, who on Sunday saw his current number one driver, Canadian Jacques Villeneuve, win the Formula One drivers' title in the last Grand Prix of the season at Jerez in Spain, also said that Senna had been an obsessive driver, someone who was always at the team to make adjustments after every practise session. "Senna was the kind of driver who would never leave you alone," he added.

Williams, however, claimed that he did not follow every technical and/or mechanical adjustment made to his cars, adding that he had not been aware of the adjustments made to Senna's steering column until after the race. Giving evidence on Tuesday, Scottish driver David Coulthard, now with the McLaren-Mercedes team, but in 1994 a test driver for Williams, told the court that he never doubted the integrity of the Williams team. Coulthard took over from Senna for some of the remainder of the 1994 season.

In particular, Coulthard argued that 20 millimetres of both horizontal and vertical "play" or movement in the Williams steering wheel at the time was normal. Much of the prosecution case is based on video footage from a tiny television camera mounted on Senna's car, showing a seemingly abnormal amount of steering wheel movement as the car entered the Tamburello bend.

Coulthard's evidence was immediately contradicted by that of former Formula One driver, Italian Michele Alboreto, who told the court on Tuesday: "I'd never have driven a car with a steering wheel that was swinging that amount".

Earlier yesterday, both Head and Newey declined to take the stand, telling the court that they reserved their right to silence but would submit written statements later.

A final session of the trial has been set for the end of November, with a verdict expected in early December. If found guilty, the defendants could face sentences of up to five years in prison. Independent legal opinion, however, suggests that all six are likely to receive suspended sentences, if found guilty.