This potentially moves the sale date from the end of March, as originally planned, to a new date at the end of May.
In an email to staff earlier this week Southgate said. "The process is progressing - rest assured we will tell you something as soon as we can.”
A spokesperson for BBC Resources said: “Mike Southgate and those in charge of the sale are looking to secure a deal that honours commitments to staff. These include pensions, no redundancies for a year, and other terms and conditions that will last for three years. This makes the sale complicated.
"It is known that bids have been made for the separate divisions of BBC Resources which further complicates the sale process."
Luke Crawley, supervisory official of broadcast union Bectu, said: “We have made our position clear, we believe it would be better for our members if a single owner bought the division. They are likely to have deeper pockets and so be better able to fulfill commitments to members.
Other factors may be making the sale difficult. These include the fact that the studios are to be closed in 2012 and the oversupply in the post industry which makes the value of these divisions difficult to pin down.
BBC staff said they expected the costumes and wigs stock to be moved from London to Oxford while the corporation tried to find another buyer.