It looks as if the arrests were preventative...if you are talking about the incident in Dudley about a month ago.
"Chief inspector Phil Dolby, from Dudley police, said: “Both protests went without incident, to my knowledge in terms of violence or disorder there were no offences.”
Police made a total of 25 arrests during the protests, 24 involved the same group of people and were made before the demonstrations began as a preventative measure to avoid a breach of the peace."
http://www.bromsgroveadvertiser.co.uk/news/droitwich_news/11778560.display/