Rod Humphris was filmed shouting at the Labour Party leader and declaring “that man is not allowed in my pub” while apparently being restrained by security.
Sir Keir left The Raven pub following the row with Mr Humphris, who told reporters that he did not agree with coronavirus lockdowns.
While in another video he can be heard “I have been a Labour voted my entire life. You have failed to be the opposition…you have failed this country.”
Sir Keir can be heard talking about his wife, who works for a central London hospital which he said had been “overwhelmed” with cases, adding: “I really don’t need lectures from you about this pandemic. Thank you.”
Sir Keir has been on the campaign trail across England ahead of local and mayoral elections taking place on May 6.
The Labour Party press office tweeted: “A clip circulating online shows Keir Starmer being confronted by someone spreading dangerous misinformation about the Covid-19 pandemic.
“We will not be amplifying it.
“Keir argued that our NHS staff have been working tirelessly to protect public health and that restrictions – while painful – have been absolutely necessary to save lives.”