A man, who was holding a bike and wearing a helmet, gatecrashed the gathering this afternoon to offer his solitary resistance to those standing guard before being rounded on by members of the group and led away.
Officers raced over to the clash point to provide a physical barrier as heated exchanges took place.
The man on the bike was then led away by several officers as some people called for him to be arrested amid the chaos that suddenly erupted.
One witness said: ‘There was a man on a bike who was shouting “you racists” and trying to incite trouble before throwing his bike.
‘I told police to arrest him like others were doing.’
A Hampshire Constabulary spokesperson confirmed no arrests were made.
A statement said: ‘A member of the public was directed away from the area by police to prevent a breach of the peace.’
Non-violent Guards of Honour Portsmouth UK, set up camp in the city centre following graffiti daubed on the Cenotaph in London.
Many in the group are veterans who wore berets and medals to make clear they were not out to cause trouble.
Mark Dolton, 57, who served with the Royal Anglian regiment in the 1980s was one of the Guards of Honour standing guard in front of the Guildhall Cenotaph.
He said: ‘I’m happy there was no vandalism and everything was in one piece. We were here to make sure no one came along and vandalised the memorials - the other crowd jumped on the bandwagon but were nothing to do with us.
‘The (memorials) are part of our history. These are people who have died during conflicts for their country. We don’t want their names defaced.
‘We accept peaceful protests but why bother smashing things up?’
Another member of Guards of Honour agreed. The veteran said: ‘Why think about causing vandalism here - it’s crazy. It’s self-defeating to their cause.’
A 34-year-old woman of Indian heritage, who lives in Somers Town, said: ‘My grandfather fought with the British during the Second World War.
‘I’m glad nothing happened to the memorials, I would be angry if it did. People should not be damaging statues and memorials anywhere.’
She added: ‘I feel like Asian people are forgotten about and Black Lives Matter has taken over.’
Alan Bradshaw, 59, who lives in the city and was among the large gatherers in Guildhall Square, said: ‘We have no objection to protest - I will stand here with you if it is peaceful.
‘We have to say enough is enough when those protests start to lead to the destruction of our heritage. Churchill and other forebears fought and delivered the freedoms we have today.’
He added: ‘You can’t judge people from history by today’s standards.’
Another man added: ‘We didn’t come here to cause trouble. We just came here to offer a guard to the statues and memorials.’
The dozens of people who turned up in Guildhall Square to protect monuments were not associated with Guards of Honour.
A demonstration planned for London has seen the statue of Winston Churchill boarded up after it was sprayed with graffiti earlier this week.