"Iain Dale asked Iain Duncan Smith about his campaign in Chingford and Woodford Green.
He faced fierce competition from Labour's Faiza Shaheen.
IDS said: "I think this was the nastiest, foulest campaign that I've ever seen fought in my 27 years in Parliament.
"We had death threats, we had threats of violence, I had women, female workers chased down the street by carloads of Labour badge-wearing young men, screaming that they're going to smash their face and deal with them.
"We had graffiti all over our office, we had a dead rat dismembered rat that came through the mail, which obviously they were hoping somebody would open.
The police had to be called in. We had all this vile abuse on on the social media, which was threats of burning the building down, sorting people out, worse to come. I mean, it was astonishing, actually."
He continued: "This cancer that has now affected body politic and I genuinely, genuinely point the finger now this Momentum crowd that have been coming in to support the Labour Party.
"They have really shifted the balance and I don't care what anyone says, it is appalling, absolutely appalling.
If people don't agree with you, the objective is now to intimidate them off the place and that's not how British politics works."
Faiza Shaheen refuted the idea that Momentum had anything to do with her campaign.
She said momentum "actually took my events off their campaign map and didn't even encourage people to come here for Election Day."
She added: "In any case, the weird demonisation of momentum is out of control. Go to a momentum event - combination of teenagers and grannies.""