It is not safe to leave a live wire unterminated behind plaster
Answered by Sarah, Electrical Safety Expert
It is not safe to leave a live wire unterminated behind plaster. If the wire is not required, then get an electrician to trace it and disconnect the wire. If the wire is required for an appliance or accessory which will be fitted later then the wiring should be prepared and terminated properly in a junction box or an accessory box with a blank plate fitted so that there is no access to the live parts.
For this type of work, we would always recommend that you use a registered electrician. This gives you the peace of mind that if something does go wrong, the work is insured and their scheme operator can help you if you are not satisfied.
You can find an electrician local to you here.