The idea of a so-called progressive alliance involving Labour and the SNP in the event of a hung parliament is "absolute nonsense", Alistair Darling has said.
The former Chancellor and leader of the Better Together campaign said there was nothing progressive about the break up of the UK and advised SNP leader Nicola Sturgeon to "get on with the day job".
Lord Darling was campaigning in Clarkston, East Renfrewshire, with Labour candidate Blair McDougall who is hoping to win back the seat Jim Murphy lost to the SNP in 2015.
As polling day nears, the Conservative lead over Labour across the UK seems to be shrinking, leading to speculation that the SNP could become involved in a ''progressive alliance'' at Westminster.
First Minister Nicola Sturgeon has said that she would be open to forming a ''progressive alternative to the Tories'' with other parties if the election delivers a hung parliament.
However, Mr Darling dismissed the idea.
He said: "There's absolutely nothing progressive about breaking up the United Kingdom, nor is there anything progressive about spending the next few years talking about a referendum when we had one three years ago when Scotland voted decisively to stay as part of the United Kingdom.
"If you look at things like health and education the nationalists' record in Scotland is atrocious.
"There's nothing progressive about educational standards going backwards, there's nothing progressive about longer waiting lists in the health service both of which the nationalists totally control, so I just think it's absolute nonsense.
"She should get on with the day job, concentrate on what she was elected to do which has been neglected in the past, and above all drop this idea of an unnecessary and unwanted referendum."
Asked his view on Jeremy Corbyn's leadership of Labour he said: "He has had a much better campaign than anyone would have said at the start of the campaign" and added that things were now much less clear cut than they were a few weeks ago.
He and Mr McDougall met with voters and activists in East Renfrewshire, the constituency Mr Murphy won from the Tories in 1997 and held until 2015.
Lord Darling said: "Throughout the UK there are many many people who are fed up with constant austerity.
"Nearly half the population voted against Brexit and during the course of the campaign the Tories have clearly fixed to the right and are trying to move the Brexit vote and have made very little attempt to reach out to the half of the population who take a very different view of the world they want to live in.
"In this election as things have developed things are not as clear cut now as they appeared to be at the start of the campaign."
Mr McDougall was the Better Together campaign director.
He said: "At the last General Election it was a straight contest between Labour and the SNP in East Renfrewshire. Despite rejecting nationalism in 2014 by overwhelmingly voting to remain in the UK, our area is represented by the SNP because the pro-Union vote was split.
"If voters in East Renfrewshire want to send Nicola Sturgeon a message that we don't want another divisive independence referendum then they have to vote Labour on June 8."