Can I prove my legal age *implicitly* so that I can drink in the UK?

I hold Swede passport and I am traveling to UK this month. I’ve read (http://news.bbc.co.uk/2/hi/uk_news/6598867.stm) that legal age of drinking alcohol in UK is 16 to 18 depending on the type of beverage.

I am an undergraduate student and look about 18. Can I use my my university card (Swede uni) in place of my passport in bar entries. Since a typical university student is 18 or above so can my university card be as a proof of age, implicitly though?

How to I prove my legal age so that I can drink in New Zealand?

I am traveling to New Zealand in the spring, and I have a question regarding alcohol consumption. The legal drinking age in the United States is 21, yet it is 18 in New Zealand. I am over the age of 18 so I plan on drinking. However, I am assuming my American ID is not going to work to prove my age, so will I use my passport? Asking any students who have studied abroad or just anyone who knows!