Some politicians in pro-Union parties are "privately enthusiastic" for Scottish independence and should be allowed to speak their minds without fear of party discipline, Green leader Patrick Harvie has said.
The MSP said he has met members of all parties who are "more open to independence than their parties will admit".
The comments were made as leaders meet to discuss the staging of the 2014 referendum, at the invitation of First Minister Alex Salmond.
Mr Harvie hopes the wider debate will not be split on party lines, allowing a free discussion on both sides.
He said: "Over the years I've met members of all parties who are more open to independence than their parties will admit, and it's not hard to find some who are privately enthusiastic.
"It's important for our democracy that they should feel free to speak their minds, and to campaign for a Yes vote without fear of party discipline.
"Independence has too often been seen as a simple split down party lines but the truth is more complex than that.
"Party leaders can sit down today and discuss the timing, the question, votes at 16 and a host of other issues. But the referendum is too important to be carved up between five people behind a closed door.
"Everyone in Scotland, including those in parties that don't support independence, must be free to campaign for the result they really believe in."