The promoters of the British Grand Prix at Silverstone have been warned they have just one chance to keep the race on the Formula 1 calendar.

Octagon Motorsports have lodged a $5m bond with the FIA, the sport's world governing body, as a guarantee that it will solve the access problems which have blighted the last two races.

The company has also promised to pay £10.6m towards road improvements around the Northamptonshire circuit in time for the race on July 7.

But FIA president Max Mosley warned that any repeat of the traffic problems would mean organisers could forget about asking to stage future races at the former airfield.

Asked how close the British Grand Prix - staged every year since the World Championship started in 1950 - had come to being lost, Mosley said: "Really very close because we felt that now the Formula 1 world championship is on a par with events like the Olympic Games and the football World Cup, it simply wasn't acceptable to run it in a place to which there was really no proper public access.

"There has been constant pressure (on organisers), but it produced no results and the only real change at Silverstone in the last ten years has been the building of a palatial clubhouse for the members of the British Racing Drivers Club, which is just a few hundred people.

"Pressure was growing from the continent and it was beginning to be said that the only reason the British Grand Prix was still on the calendar at Silverstone was because Bernie Ecclestone and I were protecting it because we were Brits, and really that began to be quite uncomfortable.

"But the thing that really precipitated the change were the events in 2000 when they were very unlucky.

"It rained very heavily and a lot of cars got stuck, but that did show up the weaknesses of the system; and then it really wasn't much better organised this year so something really had to be done."

Rob Bain, chief executive of Octagon, said he was confident the roads would be complete in time and defended the cost of tickets on sale to a limited crowd of 60,000.

"I offered to the FIA a $5m bond and I think that shows the confidence we have that the roads will be complete," Bain said.

"If you look at the finances of the sport, all we get is gate money. We have to pay a fee to Mr Ecclestone's company for the event which runs into many millions of dollars, far more than the bond itself, so the money that's left over only provides a limited opportunity to invest back in the circuit and that's been the historic problem.

"It's £200 for the weekend and it's three days of entertainment. We are having to spend £11m on the road network, outside of the $5m bond itself, to fix the ills of Silverstone. We have to spend many millions of dollars to bring the race to Silverstone, so it's a vastly expensive sport.

"We will make a profit of no more than a million dollars on this year's event."