ID as proof of age within pubs...?

In the UK, Scotland to be specific, what do people usually carry as ID for proof of age contained by pubs? Is there anything apart from a drivers license or a passport?
Go into any chain owned pub, and near will signs giving you the type of ID required, and also have forms for you to fill contained by.
Drivers Licence, government issued ID card, passport or military ID are all suitable forms of government issued identification.

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