Relatives of Ian Tomlinson stormed out of his inquest today after the police officer who pushed the newspaper seller to the ground during the G20 protests told an inquest he wanted to "help the family".
Judge Peter Thornton told Pc Simon Harwood: "I'm sure that you know and no doubt will have been advised that you are not obliged to answer any question tending to incriminate you.
"It may well be that I shall repeat that warning to you later, reminding you that you may refuse to answer a question if the answer tends to incriminate you."
Pc Harwood, dressed in a grey suit and patterned yellow tie, said: "I'm very aware of that. I'm here as a witness to help with the inquest and also to give some sort of answers to help the family.
"So I'm here to answer questions, just to help."
At this, family members including stepson Paul King walked out of the hearing room.
Mr Tomlinson's collapse on the pavement on the fringes of demonstrations in London on April 1, 2009 became global news after video footage challenged the original official version of events.
Pathologist Freddy Patel found the 47-year-old died of natural causes but amateur video later showed him being pushed to the ground by Pc Harwood.
He died after staggering about 100 yards and falling to the ground in Cornhill, near St Michael's Alley.
The inquest is being held at the International Dispute Resolution Centre in Fleet Street, London.
The inquest heard Pc Harwood rejoined the police service in November 2004, going straight into the Territorial Support Group, based in Catford.
He was asked about his understanding of how officers were allowed to use force when policing public order situations.
He said: "Use of the reasonable force always has to be justifiable by the individual, nobody else."
The inquest has seen video footage of Pc Harwood striking Mr Tomlinson with a baton before pushing him to the floor.
Mr Tomlinson can be seen turning away from a line of officers with his hands in his pockets before he is shoved in the back.
Pc Harwood told the jury officers received regular training in public order policing, about once every five weeks.
He said judging when to use a baton or to push depended on the situation the officer faced on the ground.
Pc Harwood said he had attended a large number of demonstrations during his time in the TSG.
On the day of the G20 protests he was assigned as a carrier driver.
Asked if he was disappointed to be given this role, he said: "No, never disappointed. We work as a team."
The family members later rejoined the hearing.
Pc Harwood told the inquest he was in fear of his life when a hostile crowd turned on him earlier in the day.
He said he became the centre of attention, with the protesters jeering and shouting as he tried to arrest a man on suspicion of criminal damage to one of the police vans.
The officer said there was a "large gasp" from the crowd as the suspect he had hold of collided with the door of a police van.
Footage showed him leading the man further away from the vans with the crowd surging behind him.
He said: "At the time because he was becoming more aggressive, more hostile, I was starting to believe that this was getting out of control."
He added: "I was aware there was a very hostile crowd and I was actually in fear for my life then from what was coming towards me."
Pc Harwood was asked whether, given the atmosphere in the crowd, he made the right decision to try to arrest the man.
He said the suspect had been writing on the vehicle right in front of him and added: "I believe it was my duty to go and take some course of action towards this male."
Pc Harwood said before going out on duty he had made sure his police numbers were displayed on his uniform.
He said of the feeling before the demonstration: "There was a general feeling that it would be robust policing, not just going and picking on people, but robust as in keeping the demonstration where it should be."
Earlier, Pc Harwood's supervisor, Inspector Timothy Williams, told the inquest they were in the team room in Catford a week after the protests when video footage of the incident was played on the television.
Insp Williams said: "When it came on Pc Harwood obviously looked at the footage and he said to me, 'I think that's me'.
"And I looked at him and I said, 'No, no it's not'.
"And he said to me, 'I'm not chomping, I think that's me'."
The inquest heard "chomping" is a term used among Territorial Support Group officers which means "pulling your leg".
He continued: "He did look clearly quite serious and his hands were on his head."
Insp Williams told the inquest that his understanding was that the officer had already been identified as coming from Hackney.
"Which is why I said to Pc Harwood he was wrong. I can't remember the exact words I used but he was wrong, he was being stupid. I don't know why he thought it was him because it obviously wasn't."
Insp Williams said he had been "100% convinced" it was not Pc Harwood, particularly because he had discussed the issue with a senior officer.
The inquest heard that after contacting a police federation representative, Pc Harwood was "taken ill" and did not return to work.