Britain First are an ultra far right group, they have a paramilitary wing called the "Britain First Defence Force". They organise ‘days of action’ that target a specific demographic namely Muslims, they use these days of actions to harass Muslims in shops, on the street or in mosques.
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Some of its campaigners have also been banned from every mosque in England and Wales for their actions.
http://www.independent.co.uk/news/uk/home-news/britain-first-banned-from-all-mosques-in-england-and-wales-after-police-take-out-injunction-a7196831.html