Alistair Darling has weighed into the war of words between the Scottish deputy first minister Nicola Sturgeon and the leader of CBI Scotland.
The former chancellor said Iain McMillan, the director of CBI Scotland, was being targeted by the nationalists for "having the audacity to raise questions about independence".
"It seems like the new year has not resulted in any new tactics from the nationalists. It is absolutely extraordinary that the deputy first minister of our country thinks that it is appropriate to attack someone in this manner simply for having the audacity to raise questions about independence," Darling said.
The spat between Sturgeon and McMillan erupted after the CBI chief's New Year message, in which he challenged Scottish nationalists to be "open and realistic" about the dangers of separation.
A spokesman for Sturgeon had labelled McMillan's criticism of the SNP's logic for independence as "regurgitating the same tired old scare stories".
McMillan was so incensed that he hit back at the nationalists in an interview with the Daily Telegraph in which he called the attacks on him "reprehensible" and accused the SNP of trying to discredit him through smear tactics.
He said: "It appears to be attack the messenger and don't address the problem. This has been going on for a long time and all it does is tell me and my members that they are unable to explain to business leaders their case for independence.
"The more often they do this, the more sceptical businesses will become. If the Scottish Government were confident in their arguments we would not be seeing any of this behaviour, which at times quite frankly is reprehensible."
Darling has now intervened claiming the SNP's tactics would leave them short changed when it came to convincing Scots to vote for independence on the referendum in September 2014.
Darling said: "People should be allowed to question their government without fear of this kind of attack. People should be allowed to hold a different opinion to that of their political leaders without those leaders going after them in this ridiculous manner.
"The nationalist intention is simple: abuse anyone who speaks out or even calls into question their claims or assertions. They won't succeed."
Sturgeon carried on the debate in an interview to BBC Scotland: "I firmly believes who wins the economic argument will win the referendum," she said.