LABOUR are making a potentially "fatal mistake" by treating September 18 as if it were another election instead of a referendum transcending party politics, Nicola Sturgeon has claimed.

The Deputy First Minister also said the Yes camp was making "substantial progress" in its bid to win the support of a majority of Labour voters.

Her comments came after a YouGov poll showed the Unionist side's lead falling from 22 points to six in a month. One of three pollsters which, until now, have found relatively low support for a Yes vote, YouGov also found support for Yes among previous Labour voters at a record 30%, up from 18% around the time of the first TV debate between Alex Salmond and Alistair Darling.

Sturgeon said: "One of the mistakes is to try and make out it's all Labour versus the SNP, when the population largely has moved beyond that."

But Better Together chairman Alistair Darling said: "Better Together by its very nature brings together people who disagree on many things but who agree that we should stay in the UK."

With 11 days until polling, and concerned about its core vote, Labour will deploy Gordon Brown, John Prescott, Ed Balls and Welsh First Minister Carwyn Jones in Scotland this week. Union leaders will also appeal to Labour voters at this week's TUC conference. Union leaders representing GMB, CWU, NUM, Aslef, Usdaw and Community yesterday issued a statement in support of a No vote.