First Minister Alex Salmond has again resisted calls to name a date for his planned independence referendum.
Labour leader Iain Gray said it was "fine" if the poll on Scotland's constitutional future did not take place until as late as 2016, as long as the First Minister ended the "corrosive" uncertainty by revealing when the vote would take place.
The SNP has not yet revealed the date for the referendum, with Nationalists only stating it will take place in the second half of Holyrood's five-year parliamentary term.
Mr Gray, who is standing down as Labour leader next month, raised the issue with Mr Salmond at First Minister's Questions in the Scottish Parliament.
He said that before he finished in the role he might get the SNP leader to "listen to the question".
Mr Gray said: "I asked him what is the date. If the date is 2014, 2015 or 2016 fine. Just tell us what it is.
"The longer this goes on the more it looks as if Alex Salmond is trying to rig the referendum to get the result he wants."
But Mr Salmond seized on his Labour rival's remarks, stating: "Let me just welcome the clear statement from Iain Gray that a referendum in the second part of this parliament is, I think he said that's fine.
"We shall hold him and his successor to that commitment."