The publisher of ex-Labour spin doctor Damian McBride has received a police caution after a scuffle in Brighton.
Iain Dale and anti-nuclear campaigner Stuart Holmes tussled out of shot of a live television interview on Tuesday.
Mr Holmes had been waving a poster behind Mr McBride, who was being interviewed on the seafront.
Mr Dale, 50, who has admitted common assault, apologised on his blog, saying he had "behaved in a frankly idiotic way".
He added: "I want to apologise and say sorry to Stuart Holmes, who is a passionate campaigner and well known to everyone who attends party conferences and was perfectly entitled to do as he did on Tuesday in trying to get attention for his causes."
"It was totally out of character for me to react to him in the way I did."
Mr Dale, of Biteback Publishers and from Pembury in Kent, added: "I also want to apologise for the blogpost I wrote after the incident.
"It was full of absurd bravado and in the heat of the moment I behaved in a frankly idiotic way.
"I have embarrassed not only myself but my family and my work colleagues and I apologise to them."
The confrontation was filmed by members of the media covering the arrival of Mr McBride, who was being interviewed by ITV's Daybreak programme at the time.
'Giant of a guy'
Immediately afterwards, Mr Dale - who is better known as a political blogger than a publisher - said: "In some ways I have committed the cardinal sin of becoming the story myself, rather than my author."
Mr Holmes said: "I was not ruining the interview, I was just in the background. I was not saying anything.
"Then this giant of a guy turned up and grabbed hold of me. I struggled free and in the process we ended up on the floor."
Ch Supt Paul Morrison, of Sussex Police, said: "We respect the rights of people to protest peacefully.
"We will investigate fairly any allegation regardless of who is involved and we will seek the most appropriate resolution."
The Labour Party was in Brighton for its annual conference.