Mind
Mind offer confidential help for the cost of a local call, including by providing timely information about mental health to empower people. They also offer legal support in the form of information on mental health related law to those suffering from mental health problems, as well as to those supporting them.
They have a dedicated section on their page to the issue of “Helping someone else”, which includes advice on how to support someone, how to help them seek help, and how to look after the self while caring for/helping someone else.
Download the leaflet: How to have conversations about mental health