Protesters who had gathered for a peace rally marched on a Portsmouth police station after one of their leaders was arrested.
Around 400 people turned up at Portsmouth's Guildhall Square to call for an end to Israel's attacks on Gaza.
The protest passed peacefully but ended on a controversial note when one of the organisers, campaigner John Molyneux, was arrested by police minutes before it was due to end.
Protestors, who had marched for an hour through Commercial Road to Crasswell Street, then moved round to Portsmouth Central police station to demand Mr Molyneux's release.
They only dispersed when fellow campaigner Waldemar Axim who had been allowed into the police station to check on Mr Molyneux's welfare, stood on the steps to inform the crowd that he was fine.
Mr Molyneux was later charged with an offence under the public order act because police say he had not given them the required six days notice to enable them to patrol the event effectively.
Campaigners accused the police, who were seen taking video footage of Saturday's protest, of being heavy-handed.
But police insisted their response was reasonable.
John Woods, 45, who is part of one of the organising groups – the Portsmouth Stop the War Coalition – said: 'It was definitely heavy-handed, the way they swarmed on John and then wouldn't let anyone near him.
'We were coming to the end of the protest so no one could understand why they decided then to arrest him then. Nothing could possibly have justified it.'
Angus Geddes, a co-organiser from the Portsmouth Network for the Just Settlement of the Arab-Israeli Conflict, said: 'The protest was very orderly. We tried our best not to disrupt things.
'The police seemed very co-operative at first and were walking along with us, but then all of a sudden, just as people were leaving to go home, John was arrested.
'It did seem very unnecessary. No-one was causing any problems. There was suddenly a lot of police around him, which upset the protesters because they were worried for him because he has a heart condition.'
Mr Geddes added: 'I was an organiser as well, but they seemed to choose John to arrest instead. I'm not sure why. Maybe it was better to just make the one arrest. It seemed very unnecessary.
'If it was about the short notice of the march then that seems bizarre as marches have taken place, without six days warning and without arrests, in the past.'
Jenny Lewis, 26, from Waterlooville, said: 'The protest had been so successful until the end.
'It was only thought about 30-50 people would turn out and then hundreds did and we seemed to really make a point, with shoppers genuinely stopping to see what we were protesting about.
'And the police seemed fine all along the way. They were fine in Guildhall Square and escorted the march through Commercial Road but just when people were leaving they seemed to turn.
‘I saw people running to help John because everyone was worried, but it seemed the police were pushing people away and making a barrier around him. It seemed so excessive.’
Detective Sergeant John Geden, from Hampshire Police, said: ‘I would say the policing of this event is in line with how we police all events. We understand that people have a lawful right to protest and we wouldn’t want to stop that. It is their democratic right.’
He said the arrest was only made because Mr Molyneux had not given officers proper notification on the demonstration to ensure they could not keep the streets safe.
‘This law is very sensible because it allows us to make sure people are kept safe and we were not able to do that.
‘I would like to stress that only one person was arrested and the other people behaved peacefully. It is not an issue of being heavy-handed, it is an issue of keeping the public safe.’
Mr Molyneux, who is due to appear in court later this month on the public order charge, said: ‘I want to make it clear that I think this law has a fundamental flaw because it doesn’t take into account that we have a human right to organise a protest immediately. The Israelis didn’t have to give six days notice before they started bombing Gaza.’
email@example.comCampaigner led Iraq protests
John Molyneux is a 60-year-old senior lecturer in history and theoretical studies. He also lectures in fine art.
The 60-year-old became involved in the Socialist Workers Party in 1968 and campaigned against the Vietnam war.
After studying modern history, politics and sociology at Southampton University he moved to Portsmouth in 1971.
Mr Molyneux then studied for a PhD in Political Theory at Southampton University while living in Portsmouth.
In 1992 he began working at the University of Portsmouth where he has been a lecturer in art and history ever since.
In 2001 Mr Molyneux joined the Portsmouth Stop the War Coalition.
He was the organiser in Portsmouth for the London demonstrations against the Iraq war in 2003 which saw 12 coaches leave Portsmouth for London.
He will be speaking at Southsea Community Centre this Wednesday at 8pm on behalf of the Portsmouth Socialist Workers Party.