Tony Blair has said the SNP is a “reactionary political force” with an ideology similar to that of cavemen.
The former prime minister accused the party of blaming others for Scotland’s problems, stating that nationalism is “the oldest politics in the world”.
Mr Blair made the comments during an appearance at the centre-left Progress think-tank in London.
Labour lost all but one of its Westminster seats north of the border in May’s general election as the SNP made sweeping gains.
Asked if he feared the party might disappear “just like Woolworths” from Scotland, Mr Blair said: “No, I don’t think we will. All political parties could in theory, but I don’t think we will.”
He said he had spoken with some Scottish Labour figures who were “depressed, as you would expect” following the election result.
Giving them advice felt like being someone who had spent the war at home telling veterans of the Somme how they could have done it better, he said.
Turning to the SNP, he said: “We have to take the ideology of nationalism head-on.
“Nationalism is not a new phenomenon. When they talk about it being new politics, it is the oldest politics in the world.
“It’s the politics of the first caveman council, when the caveman came out from a council where there were difficult decisions and pointed with his club across the forest and said, ‘They’re the problem, over there, that’s the problem’. It’s blaming someone else.
“However you dress it up, it’s a reactionary political force.”
Mr Blair said the nationalists had been allowed to “behave like an opposition” while in government at Holyrood.
His remarks come after the SNP argued it was the “official opposition” at Westminster after Labour decided to abstain on welfare cuts proposed by the Conservatives.
SNP MP Mhairi Black said: “Tony Blair must still be smarting from Labour losing the Scottish Parliament election to the SNP in 2007 when he was prime minister and had dragged Labour so far to the right that it was barely recognisable.
“Tony Blair’s legacy still haunts and damages Labour today, and led them into the sorry position of not even voting against the Tories’ welfare cuts and budget bills this week – leaving the SNP as the real and effective opposition to the Tory government.
“On any reading of his record, Tony Blair was the one with the primitive policy – dragging the country into an illegal war in Iraq, at the cost of hundreds of thousands of lives and causing massive instability to the region, the ramifications of which we continue to live with.
“His criticism of the SNP government suggests someone badly out of touch, presumably unaware that SNP poll ratings have reached 60% this month, but we take nothing for granted for the future.”
She added: “While Labour continue with their infighting and recriminations, the SNP will get on with the job of delivering for Scotland and working for progressive politics across the UK.”