Citizen Cards are mainly used by people who need to prove their age, rather than their identity, but they can also be useful to others:
http://www.citizencard.com/
Some accommodation providers only accept a passport (and not even a driving licence) as evidence of ID from customers who simply turn up without pre-booking. (e.g. easyHotels have that policy). However you can get round that by booking on the website of the relevant hotel company (or through an accommodation broker, such as Booking.com) prior to arrival.