Indian industrial giant Tata Motors has begun detailed discussions to buy the Jaguar and Land Rover.
Workers at Jaguar and Land Rover sites across the Midlands were told that further 'substantive discussions' would take place between Tata and Ford, which is selling the two marques.
Jaguar-Land Rover chief executive Geoff Polites said Ford was committed to "to focused negotiations at a more detailed level with Tata Motors concerning the potential sale of the combined Jaguar Land Rover business."
The letter, which was issued just after 11am, said there no final decisions had been made and there was still a considerable amount of work to do.
Mr Polites wrote: "Ford will proceed with further substantive discussions with Tata Motors over the forthcoming weeks.
"These are complex commercial discussions and Ford believes it is in the interests of all parties concerned if the process continues to be conducted in a confidential manner.
"Therefore, Ford is not discussing the content of its ongoing dialogue with Tata Motors at this point in time other than to say any final decisions Ford makes will be in the best interests of Jaguar Land Rover and Ford."
A Tata Motors spokesman said the firm had been interested in the Jaguar Land Rover business for some time. He said: "We can confirm that we have had positive discussions so far with Ford concerning the possible purchase of Jaguar Land Rover and we are now entering a period of more focused and detailed negotiations with Ford.
"We hope both parties can reach an agreement in the forthcoming weeks, though these are complex discussions and there is still much work that needs to be done before that position is reached.