Anti-Brexit campaigner Femi Oluwole said police had "dropped the ball" when Conservative MP Anna Soubry was confronted by angry protesters.
The Our Future Our Choice spokesperson filmed the confrontation, in which a group of men accused the MP of being a "fascist" and a "Nazi".
"These people represent an extreme, thuggish section of society whose aim is simply to cause division and stir progression," Mr Oluwole said on the breakfast show.
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"We need to be clear on this - these people do not represented Brexit voters."
Mr Oluwole claimed the protesters had spent "the majority of yesterday" making their views heard, with police staying "mainly on top of it" until the confrontation broke out.
"Anna Soubry has already been targeted by that guy before, especially given that they had shouted at her while she was on TV," he said.
Anna Soubry is surrounded by protesters in Westminster. Image: Femi Oluwole
"At that particular moment it was an issue of heightened risk and there should have been police protection around her, given that there was warning."
Mr Oluwole was also shouted at by the group, but told Julia Hartley-Brewer he was "kind of getting used to" facing verbal abuse.
"I get abuse online every minute, racial abuse every day, threats of violence every couple of months and in February someone posted my home address online."