Published Friday, 01 March 2013
Jim Dowson during a protest in Belfast at lunchtime. (© Pacemaker)
The 48-year-old, who was seen at a protest outside City Hall on Friday afternoon, was later detained by officers from the Operation Dulcet inquiry team.
He is being questioned on suspicion of offences linked to the ongoing flags demonstrations.
Willie Frazer and Jamie Bryson, both key figures in organising the protests, were arrested earlier in the week as part of the same investigation.
Mr Frazer was remanded in custody after appearing court on six charges on Friday.
The protests have been taking place across Northern Ireland since December when Belfast City Council voted to reduce the number of days it flies the Union flag.
Police asked motorists to avoid city centre at around 1pm after a group of around 200 people gathered, causing "severe disruption" to traffic.
Protestors stayed on the footpath at the front of City Hall in a peaceful demonstration for an hour, according to PSNI.
"Police prevented any attempt to parade by blocking Chicester Street for a short period of time," a spokesperson said.
Around 100 protestors then assembled at the bottom of the gates outside Stormont amid a heavy police presence.
Two members of the group were escorted up into the building where they delivered a letter of protest addressed to First Minister Peter Robinson.
They were cheered as they left the building, then the crowd moved away from Stormont.
Police say the peaceful protest ended at around 4.30pm.