XXXXXXXX,
The level of aggression and violence that your son is showing, in addition to the mood symptoms you've described, makes this an emergency situation. I would suggest that you take your son to an emergency mental health facility for immediate evaluation (either a hospital or crisis center). You and your husband cannot manage your son's symptoms on your own and he requires further help than you can give. If you cannot get him to go with you to one of these facilities I would suggest that you call the police and explain the situation. (I don't know how it works in the UK, but in the US the police can sign an order of involuntary hospitalization which means that the person is required to go to a psychiatric facility for further evaluation. The hospital can then determine whether or not he needs to stay there for treatment or receive outpatient treatment somewhere else.)
Psychologist
Doctorate in Clinical Psychology, 10 years experience working with individuals, couples, & families