The Electoral Commission asked both administrations to reach a shared position by today.
John McCormick, Electoral Commissioner for Scotland, said: "During our assessment of the question we found that people wanted impartial information about the referendum before they voted, so we asked both governments to agree a joint position on the process that will follow the referendum.
"We asked for this to be agreed by December 20 to coincide with the expected timing of Royal Assent of the Referendum Bill so that all the rules about how the referendum is conducted, and what happens afterwards, are clear at the same time.
"Now that we have Royal Assent we would like this clarity to be provided as soon as possible and we understand from both governments that progress is being made. In the interests of voters, we would ask that every effort is made to reach agreement early in the new year."
The referendum is on September 18 next year. The question will be: "Should Scotland be an independent country?"
First Minister Alex Salmond said some progress is being made between governments.
"But the central difficulty here is quite simple," he told BBC Radio Scotland.
"The only institution of state which has been prepared to have technical discussions with the Scottish Government in terms of proposals for a Yes vote or the aftermath of a Yes vote is the Bank of England where Mervyn King authorised his officials to have these technical discussions because, of course, the Bank of England is independent from the Westminster Government and, therefore, he could do that.
"But no other government department in London is prepared to even have technical discussions up until now. I hope they revise that opinion because obviously what the Electoral Commission was seeking, not in terms of pre-negotiation, but certainly technical discussions would be of great benefit in giving people some outline of the immediate implications of the negotiations that will follow a Yes vote next year."