The leader of Scotland's campaign for independence failed to turn a U.S.-style television debate into a victory for his cause on Tuesday, six weeks before Scots vote on whether to break up the United Kingdom.

In an unexpected setback for those who support a breakaway, Alex Salmond, the leader of the pro-independence Scottish National Party (SNP), didn't land a knockout blow in a lively debate against Alistair Darling, the leader of the campaign to keep Scotland in the U.K.

With the pro-independence camp trailing in opinion polls ahead of a Sept. 18 referendum that will decide whether Scotland breaks its 307-year union with England, most commentators had predicted Salmond, a powerful speaker, would notch up a rhetorical victory to breathe new life into his campaign.