Formula One's governing body has made teams a final offer, with changes to the controversial 2010 rules, in a bid to prevent the sport from tearing itself apart.

Five of the existing 10 teams - championship leaders Brawn, BMW-Sauber, McLaren, Renault and Toyota - risk exclusion if they do not sign up by today's deadline.

Should they fail to do so, there is a risk of them setting up a rival series with champions Ferrari and the two Red Bull teams also at loggerheads with the International Automobile Federation (FIA).

Both sides are making last-ditch efforts to reach a compromise deal, however.

In a letter to the provisional teams which was seen by Reuters yesterday, FIA president Max Mosley set out what the FIA was willing to concede in return for unconditional entries.

The terms effectively set in stone agreements reached before talks broke down this week, when the FIA said the regulations remained in force and accused the teams of wanting to take over the sport.

Changes included substituting an optional £40 million budget cap with a €100 million one for 2010, that figure dropping to €45 million in 2011.

"There will be self-reporting of compliance using a reputable auditor," he added, in a move to overcome the manufacturers' resistance to opening their books to the governing body.

"Any suspicions of breach would be investigated by a mutually acceptable auditor of suitable standing."

Teams indicated on Wednesday that they were prepared to accept such an independent auditor.

Mosley asked them to agree in return to be bound by the terms of the 1998 Concorde Agreement that has now expired.

The agreement would run until the end of 2014 or the signing of a new one by all parties.