Both the Conservatives and Liberal Democrats ducked the chance to appear on next month's head-to-head debate on STV about welfare and pensions.
Instead, in a group decision by the pro-Union parties, Scottish Labour's deputy leader Anas Sarwar, above, will speak for the No campaign.
Deputy First Minister Nicola Sturgeon, who was widely seen as trumping LibDem Scottish Secretary Michael Moore in the first STV debate in May, will again appear for the SNP.
The SNP claimed Sarwar was being put forward "to bat in defence of the bedroom tax", the cut in housing benefit that since April has affected about 100,000 Scottish social tenants deemed to have spare bedrooms.
Labour has never supported the bedroom tax, and rejected the policy while in office.
Sarwar, the MP for Glasgow Central, has also marched against it, calling it "government gone mad" and "a piece of backward ideological thinking from a Tory government".
However, Labour has not vowed to end the bedroom tax if it wins the 2015 General Election - though it has not ruled out abolition either - while the SNP says it would scrap it in the event of independence.
Better Together said the reaction to the STV debate was an "utterly desperate" distraction from the Scottish Government's lack of homework on how an independent Scotland would finance its own welfare and pensions system.
Sturgeon said: "It speaks volumes that both parties in the UK Government are running away from debating their welfare and pensions policies - but it is hardly surprising given how deeply unpopular those punitive policies are.
"However, people will be shocked that Labour are prepared to do their work for them, and that Anas Sarwar has been sent in to bat in defence of the bedroom tax."
Responding on behalf of Labour and the Coalition parties, a spokesman for the Better Together campaign said: "Is this really what the people of Scotland want from their government?
"Rather than getting on with her job, or answering questions people have about independence, the Deputy First Minister is moaning about who is going to appear with her on a TV show. It is utterly desperate."
A spokesperson for STV said: "Scotland Tonight is providing a platform for debate on all the issues in the run-up to the referendum in 2014 and we welcome participation from both the Yes and No campaigns. The first Scotland Tonight special peaked at almost 190,000 viewers and held the audience share well throughout the hour-long programme."