Jordan Grand Prix yesterday sent shock waves through the Formula One paddock by sacking lead driver Heinz-Harald Frentzen with immediate effect.

Just before lunchtime the Irish team issued a terse statement confirming Frentzen's contract was being terminated for the remaining six races of the season and for 2002.

"It has been a disappointing season for both of us," said team owner Eddie Jordan. "We had an exchange of views following the British Grand Prix and this is the outcome."

The "exchange of views" is believed to have been more of a stand-up row following Frentzen's disappointing run to seventh at the recent British Grand Prix. Following the race, which saw Frentzen start from fifth before slipping throughout the race, the German explained that during an attempt to overtake Sauber's Nick Heidfeld he had felt something break on his EJ11 and thereafter suffered massive understeer which prevented him from staging further assaults on the points places.

That was deemed unacceptable by the team, however, and while it is believed Frentzen did have a problem with a bargeboard, his ever-slackening times in the closing stages were judged an excessive response to the problem.

Frentzen's problems at Jordan go back almost two years, to a 2000 season begun with the memory of a stunning 1999 fresh in the memory. Frentzen's maiden year at Jordan was characterised by a string of stunning drives which earned him two wins - at Magny Cours and Monza - 55 championship points and secured third places in the drivers' and constructors' championships for Frentzen and Jordan.

That never happened. The EJ10 turned out to be too radical a design and a succession of problems, most notably with a fragile gearbox, pushed Jordan down to a dismal sixth by the end of the year. Frentzen, slumped to ninth in the drivers' championship, with just 11 points.

Frentzen's disastrous 2000 season was again followed by high hopes for this year, and at this season's launch, he branded the EJ11 the best car he had ever driven.

He took points in three of the first four races but since crashing out in Spain after being dropped to the back of the grid by a launch control failure on the reintroduction of driver aids, he has disappeared from view.

Jordan, though, appeared until yesterday to be prepared to stand by their troubled number one. Following intense speculation in the run-up to the European Grand Prix that Frentzen was being pursued by 2002 debutants Toyota, Jordan issued a statement denying the rumours and insisting Frentzen would race for them next year.

That scenario was he was surprised by his dismissal. "The reasons I have been given for the termination, I contest in their entirety," he said. "My position in this matter is now under legal advice."

That Frentzen is seeking recourse to the law would suggest a contract was signed between Jordan and Frentzen and there may be more at stake than Frentzen's appearance at the last six races of the season. Regardless of the possible financial wrangling, the timing of the German's dismissal couldn't be less fortuitous, with the team already en route to Hockenheim for Frentzen's home race, a venue where Frentzen would be the star attraction for the team's Germany-based sponsors.

Test driver and former BAR driver Ricardo Zonta will take Frentzen's place in the EJ11 this weekend and while the team would not confirm his status for the following five races, Zonta's management yesterday said they were sure the Brazilian would sit in until after the season-closing Japanese Grand Prix.

The Brazilian's placement in the car is merely a stop-gap, however. Pairing the adequate but unstarry Zonta with Jarno Trulli will leave the team no worse or better off than if they had persisted with Frentzen.

The crunch will come at the end of the season, when a genuine replacement must be found. At the moment, genuine contenders are few and far between.

The situation for Jordan could get even more desperate if the still circulating rumours that Trulli will move to Benetton prove true. The Italian, who has been critical of Jordan's commitment and focus in recent weeks, has still not signed on for another year and thus a possible move to Benetton, and Flavio Briatore, to whom he is contracted, still holds currency.

Frentzen's future, too, is unsure. Whatever about the truth of the rumoured link with Toyota before, the Japanese team yesterday denied any interest in the German driver.

When he joined Jordan in 1999, Frentzen admitted he had contemplated a move to the US in his final year with Williams and was attracted by the US Cart series. He may yet go west.