Angus Robertson said legal advice was not discussed in Holyrood except in exceptional circumstances.
Scotland’s Constitution Secretary, Angus Robertson, refused three times to confirm if advice has been sought on legislating for another independence referendum.
It is not yet known when the legislation will be published.
But the legal competence of the legislation has been questioned, with opponents claiming the ability to call another referendum does not lie in Edinburgh.
Repeated requests from opposition MSPs and journalists looking to find out if legal advice has been taken, and what the content of such advice reveals, have been rebuffed.
In a heated exchange in the chamber, Mr Robertson repeatedly refused to answer if legal advice had been sought.
Responding to Tory MSP, Donald Cameron, the Constitution Secretary said: “It’s a long established convention of this and previous Governments that legal advice is not disclosed other than in exceptional circumstances, this reflects the public interest in the provision of free and frank legal advice, maintaining the right to confidentiality of communications between legal advisers and clients.”
After Mr Cameron pushed the SNP MSP, stressing he was “not looking for the content of any legal advice”, Mr Robertson responded: “I’m going to rest on the answer that I gave previously to the learned gentleman who, as a member of the Faculty of Advocates is well aware of the custom and practice in relation to the convention on legal advice.
“I’m not going to depart from that tradition today.”
Mr Robertson was pressed two more times on Thursday, by Lib Dem MSP, Willie Rennie, and Tory MSP, Jamie Halcro Johnston, but both times refused to answer.
He told Mr Rennie, who said it was “extraordinary” the question could not be answered, his answer had not changed.
“Rather than reading out the question he wrote before arriving, perhaps he would have listened to the answer I gave earlier, and I rest by it,” Mr Robertson said.
When Mr Johnston attempted again – claiming “secrecy has trumped transparency” – the Constitution Secretary added: “It’s a curious thing, now we have a third member who didn’t listen to the answer to the question.”
Mr Robertson then read out the answer he had given to Mr Cameron.