LONDON , England ( CNN ) -- Protesters threw bricks and bottles Friday at police outside a mosque in London after about 1,000 people showed up to counter a planned a right-wing demonstration there , police said . Police arrest a protestor in Harrow , London , after fighting broke out at a planned right-wing demonstration . One person was arrested `` to prevent a breach of the peace , '' police said in a statement . The right-wing demonstration 's organizer , Stop Islamisation of Europe ( SIOE ) , said on its Web site one of the demonstration 's planners had been arrested . Seven other people were arrested during the melee for possession of `` offensive weapons '' -- including bottles of bleach , a hammer and a chisel , police said . Police said incidents at the scene began when the crowd -- believed to be either members of an anti-fascism group or there to provide support to the Harrow Central Mosque -- went after three youths , `` caught up with them , and assaulted them , '' police said . `` Police had to intervene to prevent the crowd from continuing with their attack . '' It was not immediately known if the youths were affiliated with any political group . Police said they had identified and stopped a number of people believed to be heading to the right-wing protest prior to the demonstration 's start time , preventing them from reaching the area . It was not immediately known how many , if any , of the group 's supporters had successfully arrived outside the mosque . `` One person was arrested to prevent a breach of the peace as police believed if the SIOE demonstration started it would have resulted in serious disorder , '' police said . The group said on its Web site that the demonstration had been called off and that Stephen Gash , listed as one of the group 's contacts , had been arrested `` to prevent a breach of the peace . '' `` If you are on your way to the demo , do n't go , it 's being called off right now , '' the post read . `` The police ca n't handle the muslim counter demonstrators [ sic ] . '' The group describes itself on its Web site as an alliance of people `` with the single aim of preventing Islam becoming a dominant political force in Europe . '' CNN 's Phil Black contributed to this report .
Seven people arrested for having weapons like knives , a hammer , chisel . Leader of the protest was arrested ` ` to prevent a breach of the peace '' Seven people showed up to counter a planned a right - wing protest . Official site says group does n't want Islam to be ` ` dominant political force in Europe ''