John Reid has accused Alex Salmond of indulging in anti-English sentiment to win independence votes.
The former defence secretary laid the charge directly at the SNP leader's door, accusing him of signalling to supporters last week.
Mr Reid also said the First Minister should be "ashamed" of himself for scaring Scots about the future of the NHS service and warned they were just five days left to save it with a No vote.
But the Labour "big beast" also raised eyebrows when he told Scots "if you don't know ... don't vote".
He later insisted that had been a "slip of the tongue" and he had meant to say: "If you don't know, vote no".
Mr Salmond has denied that the independence campaign is anti-English, insisting that his vision of Scottishness is inclusive.
Mr Reid told an invited audience at Edinburgh's Glasshouse that many within Labour had felt insulted last week when Mr Salmond dubbed a group of English and Welsh Labour MPs campaigning in Glasgow "Team Westminster" and contrasted them with his proposed "Team Scotland" after a Yes vote.
Other SNP politicians also referred to "Team Westminster".
Mr Reid said: "We know what they meant by Team Westminster, don't we..? They meant English.
"You cannot build a decent, prosperous Scottish society on the basis of resentment."
The former Health Secretary also called on voters not to back Yes as a "protest" against Westminster.
And he said that the best way to protect the NHS is to "vote No on Thursday and Labour next year".
SNP MSP Dr Aileen McLeod said: ""The risk to the NHS from a No vote is one of the reasons why more and more people in Scotland are switching from No to Yes.
"The more desperate the claims from Westminster establishment figures like Lord Reid become, the less attention people in Scotland are paying to them."
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