I don't understand how anybody cannot know about I.D. being needed - I seem to have known for years (or so it feels). I'm glad that bus passes are acceptable, because otherwise I would have a problem as my passport and driving licence are in my maiden name.
This actually could catch out a lot of women, who would need to take along their wedding cert..
Having said that, it has been advertised for ages (over a year I think) that you can apply to your local council for a suitable proof of identity. It was seen as patently obvious when I lived in France, that you had to bring along some proof of your right to vote.