Underweight Button escapes penalty.

Jenson Button has held on to his third place result in the San Marino GP, despite the car being found to be underweight in post-race scrutineering.

Button's car was in the scrutineering bay for several hours after the race, until it was pushed into parc ferme. The official results for the race were not published until 10.10pm, more than six hours after the end of the event.

The FIA announced that the stewards had 'after hearing the explanation of the competitor's representatives and studying all available documentation decided that the matter requires no further action.'

Usually, the cars are weighed at the end of the race just as they finish, with any remaining fuel on board. The drivers are also weighed, and the resulting calculation shows whether the car is above the 600kg limit, including the driver.

However, the FIA also reserves the right to do extra spot checks on cars that involve draining all the fuel out and reweighing them. At Imola, Button's car was selected for such a check. While it passed with the fuel on board, it proved to be underweight once the fuel was pumped out.

The implication therefore was that the team has been using fuel as ballast, which is not permitted. In other words, it only made the limit with the fuel that was left in the car at the finish, and therefore the clear implication is that it could have run at times during the first two stints of the race at less than 600kg - a strategy that is, of course, illegal.

BAR denied any wrongdoing, and it is thought that the team's available documentation involved the team attempting to prove to the stewards that the car did still have enough fuel on board when it made its first and second stops.

Although this makes no logical sense, apparently the stewards believed the team's explanation. Had the decision gone the other way, BAR Honda would have in effect been exposed for deliberately cheating.

We understand that, despite the decision, the matter might not be over...