@xahteiwi It's a ridiculous requirement (all voters should be actively and automatically registered and eligible to vote, the onus is on the government to make this as low barrier as feasible).
But if the system is as such, and one is privileged enough to be able to do so without undue effort, I think there's a moral obligation to - laziness and disinterest aren't awesome and show a lack of care for others.
HOW
???
The authorities don't generally know who people are or where they live - unless they register to vote. So no, voters can't be "automatically" registered.
In practice it is very easy and people usually don't need to do anything to stay registered.
I think Europeans in general find it very difficult to get their heads around the implications of not having a national ID system. Which is an entirely different topic of debate.
@regordane Ahum. Let me introduce you to the general residence register (in Austria: Zentrales Melderegister or ZMR). So yes, in some countries the authorities absolutely do know where people live.
The UK has a very laxidazical approach to identity.
In many ways each govt department has their own approach to identity and often their own reference numbers.
The concept of a national id scheme was floated under Blair, but was very unpopular, for many reasons.
As such the election system effectively maintains it's own list of people, as does many other govt departments.