A survey by Citizens Advice found family and friends were around three times as likely to be aware of it than the police.
Around one in five of those who knew about abuse said not knowing what to do, or who to contact, would put them off alerting the authorities, though.
Speaking about the findings Citizens Advice chief executive Gillian Guy said: "A supportive ally can provide a lifeline to someone trapped in an abusive relationship. When someone manipulates their partner's emotions, controls their finances and even physically assaults them, victims may feel too afraid or defeated to reach out themselves.
"Friends and family are often the only ones who might suspect someone is suffering behind closed doors. The lives of victims are at risk whilst they remain in an abusive relationship, so those aware of domestic abuse need to know what steps to take to provide support. People need the equivalent of a green cross code for helping victims of domestic abuse."
Vicky Walker is a Christian and campaigns on the issue of domestic violence after her friend was murdered by her partner.
Speaking to Premier, she called for Christians to become better informed on the subject.
"There are resources like oneinfourwomen.com which actually help people understand how they can support someone going through this," she said. "It's not as simple as to say 'well why don't you just leave?', there could be children involved, there could be financial dependency."
Discussing the role of the Church in this issue she said: "The church could definitely become a safer place for people who are experiencing abuse.
"We have to recognise that there are people in churches who are abusers as well. The idea that you can't be turning up to church every Sunday and not going home and behaving terribly to your partner and family, is something we have to overcome very quickly."
Citizens Advice is encouraging people to visit its website www.citizensadvice.org.uk to find more information about how they can help friends and family who may be suffering from domestic abuse.
Listen to Vicky Walker speaking to Premier's Marcus Jones.