Prost reveals why Heidfeld was disqualified

The 23-year-old German F3000 champion is barred from starting his home race after his car was found to be two kilos below the 600 kilo limit.

The decision was the latest in a series of blows as the four-times champion continues his three-year battle to take France's only F1 team back to full competitiveness despite a long-running row with Peugeot over the competitiveness of their V10.

"Unfortunately we made a mistake in calculating the car's weight," said Prost. "Taking into account the new parts we had to put onto Nick's car for the first time we did not leave sufficient margin for error.

"We were one kilo (sic) below the regulation weight and the regulations are very clear - the sanction is exclusion from the event and we are not going to make any appeal against this decision.

"It is obviously tough for the whole team. Now it is up to us to put this behind us and get on with the rest of the season.

"I am sincerely sorry for Nick who has done so much positive work in the last few weeks. This is a circuit where we thought we would be able to do something in the race as the car behaves well in mixed circuit conditions."

Heidfeld said he still felt frustrated about being excluded but said the signs for the future were promising.

"I have mixed feeling today, but unfortunately the bad feelings are stronger because I cannot take part in the race, which is frustrating for a driver.

"It is going to be hard watching the others racing knowing I had a good position on the grid and a good car and that I could have obtained a good result at my home Grand Prix.

"On the other hand it is very encouraging being 13th, and at one stage ninth. That gives me reason to be optimistic for the coming races."