Motorsport boss Max Mosley has welcomed a cost-cutting initiative by Formula One teams but says more could be done.
All of the teams, with the exception of Ferrari, have agreed to a money-saving scheme which could help ensure the future of the British Grand Prix.
"That they are thinking along those lines is a step forward," Mosley, the president of governing body the FIA, told The Times newspaper.
"The point is that we now need to do much more."
The team principals agreed at the weekend measures designed to save money which could see the British GP at Silverstone included in an extended 19-race calendar.
But the deal did not secure the required unanimity because Ferrari have not signed up.
Ferrari are traditionally hostile to cuts in testing, the centrepiece of the proposals, but Ferrari sporting director Jean Todt said his team had not been invited to attend the meeting to thrash out the deal.
Mosley warned any plans would have to be geared towards the long-term development of the sport.
"I have been trying to get teams to talk seriously about reducing costs for the past three years," added Mosley.
"It is a bit too late to implement these measures for next year, but we could for 2006.
"We are in a situation where teams need 1,000 people to put two cars on the grid and that level of spending is unsustainable."
He added: "It is a completely rational plan, but the truth of it is that the teams' proposal is a minor matter and an irrelevance.
"What would be interesting was if we had a package for 2005 that got us our 20 cars. And we haven't got that.
"The three teams we are going to lose (following Ford's decision to sell Jaguar and engine builder Cosworth) won't save money, because they don't test.
"It's a piddling package compared to the problem of keeping those three teams in business."
Futher questions have been raised about the future of F1 by reports of renewed threats from a handful of teams to set up a rival series.
The Grand Prix World Championship (GPWC) - a company set up by some of the car manufacturers in F1 - is said to be ready to announce fresh plans to run a breakaway competition in 2008.
It is the latest offensive in an ongoing dispute between the teams and F1 supremo Bernie Ecclestone.
GPWC - which includes Fiat (Ferrari), Renault, BMW (Williams) and Mercedes (McLaren) - wants a bigger share of the power and profits generated by the sport.
The Concorde Agreement, the secret document that governs F1, expires at the end of the 2007 season.