I remember the movie was in black and white, possible around the late 60's and may have been set in England (I seem to remember an accent). The plot was a gang that figured out how to live forever. The idea was to "believe" you would come back from the dead, so they would each commit suicide to achieve immortality. There was one holdout in the gang that would not do it so they all got together trying to convince this last member to do it. The last part of the movie was all the "dead" members turning to stone in front of the last "living" member.

I know this is pretty vague but reading other posts I have confidence someone will come up with an answer.

Keep up the great work.