most people here in the UK would have a credit or debit card on them. almost everyone have a driver's licence, but bank cards are a must even for those that dont
That does not mean they have to carry said stuff with them. Also, credit/debit cards do not store the same kind of information an ID card stores, particularly as there is no photo.
Do you really think we ought to have a society in which no one can leave his house without his dog tag?
It's extremely normal to travel without any kind of ID, especially photo id. The main thing a lot of people carry is their driver's license, but if you don't have one of those you might very legitimately have none.