Theissen frustrated by testing restriction

Vettel had been due to take part in most of the Friday sessions this year to help increase his experience of F1 machinery. But BMW Sauber changed their plans ahead of this weekend's Spanish Grand Prix after feeling it was better for the team to utilize only their race drivers in the practice sessions.

Theissen has said that the change of plan was forced on him because of the way that the Friday sessions have turned into extended practice, rather than the day of testing that was originally planned.

"For me it was quite a tough decision to make because I really wanted to give Sebastian track experience," said Theissen. "But it has become more difficult than I expected, especially during the season with the strong reduction of testing.

"I have to say that we reviewed the situation after the first three races. And especially in Malaysia, when we were not well sorted on Friday, we would have benefited from having Nick (Heidfeld) in the car in the morning. So that was the main argument."

Theissen has said he wants team principals to talk about ways to improve the situation for 2008.

"I think it would be good to discuss it," he said. "Other team principals have discovered as well that there is just not enough opportunity to bring on young drivers, and give them what it takes to make a successful entrance to F1. There is just not enough track time.

"It started when the original idea of Friday as a test day faded away by restricting the time and limiting the car - and calling it part of the event, which means the car has to be within the regulations at all time.

"So in fact we don't have Friday as a test day, only an extended practice day. But if we changed that and allowed for more time with different cars, and even made it mandatory to get a third driver on the track, then that would help."

Theissen has not ruled out running Vettel in Friday sessions later in the year, with the German also set to get more testing away from race weekends.

"It is not decided," said Theissen about Vettel running again on a Friday. "We will review it on a race-by-race basis.

"There have been races where it has been clear from the beginning that Sebastian won't be driving like Bahrain and Monaco, because he will be with the World Series. But other than that we will have a look on a race-by-race basis."