This is one place I highly recommend if you are suicidal in London.

I missed my appointment, at the weekend just gone, due to depression.

I received phone calls from the receptionist, my counsellor to check on my welfare and I shall be receiving a phone call this Saturday. I have also an appointment to see my counsellor on Christmas Eve.

They're all volunteers and you can self-refer.

Check them out here: The Listening Place

They really do listen and they really do care about you.