Historically, whenever governments have wanted to implement an unpopular change, they have turned to the church. The fear of disobedience that religious doctrine instills in a population from birth is a powerful one and was an excellent tool in controlling behavioural persuasion.
Today, with declining religious beliefs, and increased personal enlightenment due largely to the internet, this method is rendered less useful. So governments (and large corporations) use other methods to spread fear in order to achieve their aims (the terrorist threat level is now "Yellow"). The age old rule of how to implement a deeply unpopular change is to implement it slowly - allowing the population time to accept each incremental intrusion into their lives. Thus there are
PR firms specializing in advising companies and governments on how to best achieve their fiercely-opposed aims.
My guess is that the real reason behind the introduction of ID cards is solely to enhance tax revenue collection, by aiding the tracking of both domestic & international money movements. Nothing else can substantiate the cost of implementation. There will be other ancillary advantages for the Government such as cross-referencing benefits claims and health records. Of course, none of this can be officially announced because of the certain ensuing public uproar.
The simplest way to implement such a change is to begin by spreading fear (the threat level is now "Red with orange stripes"). Fear of terrorism is the easiest to use since it is entirely speculative and the Government has a strong reason for not substantiating their claims ("Trust us. We can't tell you why but you should all be very afraid.") and my personal favourite, "It's not a matter of if but when".
Once you've spread the fear, the next step is to start countering that fear with a "trial run" over a "limited period" with a small "sub-set" of the population. A good choice would be a generally law-abiding group, whose obedience to rules is already closely monitored anyway, and whose income stream is totally dependent on their compliance. Pilots fit this description perfectly.
The next step will be to continue the trial on a voluntary basis, expanding it to other groups. After all, the threat of terrorism still exists - it cannot be proven otherwise (the threat level is now "Purple with gold polker-dots").
At around about this point, the "Passport Office" would quietly be renamed to the "Passport & Identity Office"
Then will come the complete integration with everything we do (still just on a voluntary basis), opening a bank account, visiting your doctors surgery, enrolling your kids at school, filing your tax return.
Then, quietly, buried at the bottom of more lengthy "Anti-terror" legislation - the system finally become compulsory.
Et voila ... the change has been implemented and every law-abiding citizen now has something to scrape the ice off the windshield in the mornings.