Ed Miliband claimed the campaign for independence has an "ugly side" during chaotic scenes as he was mobbed during a visit to Edinburgh.
The Labour leader took his fight to save the union to the St James Shopping Centre in the city but struggled to talk to voters as campaigners from both the Yes and No camps clashed.
Labour had attempted to keep details of the visit quiet to prevent it being hijacked but Miliband found himself surrounded by media and campaigners as well as members of the public.
Chants of "Vote Yes" and "You're a liar" competed with chants of "Vote No" as shoppers were trampled and pushed aside.
Miliband told the BBC: "I think we have seen in parts of this campaign an ugly side to it from the Yes campaign.
"I think debates should be conducted in a civilised way, I think that's very, very important, but I understand that passions run high. What I've enjoyed about this campaign, including today when I get the chance, is meeting people who are genuinely undecided."
Labour MSP Kezia Dugdale, who was on the scene, later tweeted: "Campaign room full of visibly shaken and upset folk who were in St James Centre - truly crappy day for democracy."
Miliband spoke briefly to a handful of voters before the chaotic visit was brought to an end. He told reporters: "If people vote no, it's for change and more powers for a stronger Scotland, as well as NHS funding guarantees, and that's got to be weighed against the big risks of voting yes. That has been the choice that people are facing in these last couple of days in this referendum campaign."
He added: "I think that the momentum is with the No campaign as people recognise that there is a clear offer of change by voting No."
Asked if he was making it up as he was going along, he said: "Not at all. We have set out very clearly throughout this campaign that there will be more powers for the Scottish Parliament, that this is the choice on offer by voting No against the big risks of voting Yes."