We had them after WWII until sometime in the 50's when they were removed due to abuse by the authorities. Hence there is still a distrust of them. The scheme recently introduced and then scrapped could have had some interesting consequences.
This is part of why we have such "fun" with the free movement provisions, in that we do not have a population register. Nor a requirement to keep the authorities notified of where we live.
Hence unlike the other EU countries, we can not enforce the 90 day limit on EU folks being here without means to support themselves.
http://news.bbc.co.uk/1/hi/magazine/3129302.stm
a bit more detail here:
http://www.historyandpolicy.org/policy-papers/papers/identit...
It is rather a pointless exercise, since people can slip past the border, and once within the country there is no need to carry or produce ID. So as long as one avoids interactions with the authorities, one will not be tracked.
About all it will do is allow a count to be kept of the number of law abiding (non EEA & non Swiss) foreigners within the country.
If Brexit ever does occur, it may then also include the EEA countries and Switzerland (depending upon what reciprocal travel arrangements develop), but would not include the Irish.
Any idea what the punishment is for not carrying?
In practice, that means you just carry your regular driver's license in your wallet when crossing the border.
I hear there's a similar setup in the Benelux countries, so ID is definitely not mandatory in the entire EU.
Now, there aren't any checks except for the border into Sweden from Denmark, but if there is a check you are not allowed to travel using an ID or driver's license. Driver's licences, ID cards issued by banks or tax offices are not valid for travel within schengen even though you are generally able to move between the countries anyway.
The misconception you present is the reason Swedes with driver's licences and normal ID cards got stranded in Denmark.
"Within the Nordic area, any Nordic identity documentation (e.g. a driving license) is valid as proof of identity for Nordic citizens because of the Nordic Passport Union, while a national identity card or a passport is can be required in other Schengen countries"
https://en.wikipedia.org/wiki/Nordic_Passport_Union
In other words, you need to be able to identify yourself, but not necessarily with a national ID or a passport as you would when entering other parts of the Schengen area.
The border controls between Denmark and Sweden are a temporary suspension of those rules but it only concerns people crossing the border at those points -- not people who who are already in the country or people who cross the borders at other locations, like say, the Finnish/Swedish border.
Mind you I suspect mostly people do carry 'official' identification documents on them most of the time (e.g. driving licenses) but there is no requirement to actually have these on you at all times.
"if you've done nothing wrong, you've got nothing to fear / if you've something to hide, you shouldn't even be here"