If they have been violent against others then this might constitute a sufficient ground for section 8 eviction. You can fill out an application to the court to possibly obtain an eviction order under ground 14 (the individual has been guilty of conduct causing or likely to cause a nuisance or annoyance to a person residing, visiting or otherwise engaging in a lawful activity in the locality). However, because this is a discretionary ground the court will make the eviction order only if it is reasonable to do so. If awarded then the tenant is obliged to leave after 2 weeks, after which possession proceedings can be started.