Crewe Motors, the consortium of Rolls-Royce and Bentley owners attempting to put together a last-minute bid, said yesterday that it still hoped to table an offer by Friday.
The consortium's advisers have had discussions with Vickers' financial advisers Lazard Brothers and a bid of more than pounds 430m has been discussed.
But Michael Shrimpton, the barrister heading Crewe Motors, said it would take longer than Friday to secure letters of credit and other legally binding assurances from his backers, said to include a British clearing bank and a US billionaire.
"What I can't promise is to match VW this week,'' Mr Shrimpton said.
In the absence of a cast-iron unconditional bid, Vickers will proceed with its extraordinary shareholders' meeting, due to take place tomorrow morning at the Royal Horticultural Halls in central London.
"We still have not got a formal offer so we are going ahead as planned," said a Vickers spokesman. "We do not take kindly to the idea of postponing the meeting and we cannot see that it will be knocked off course."
If the meeting went ahead and shareholders approved the sale of R-RMC to VW then would be the end of the matter. "There comes a point at which we reach the end of the road and that would be it," the spokesman added.
Earlier this week Vickers said that if the meeting was delayed then the earliest the sale could be completed was September. That would create risks and uncertainties for the business.
Vickers says that the total value of the VW bid is likely to be between pounds 460m and pounds 470m including working capital injected into R-RMC since the start of the year which the German car-maker will fund.