His argument seems to be, that it's just like a driving licence or passport, and you have to pay for those. But it is not like either of those if it is compulsory. People can choose not to have a driving licence or passport, and choosing to have one of those documents is an implicit sign that you can afford it (as you are going to be doing something with a motor vehicle, or travelling abroad, neither of which are cheap).
Furthermore, he seemed on Channel 4 News, adamant that ID cards should not be paid for out of general taxation (maybe that's because Mr Brown isn't too keen on them, or maybe it's just because Mr Brown doesn't like spending money). But if you're going to enforce ID cards and require everyone to pay a flat fee for them, isn't that taxation by stealth? (err, actually, it sounds more like a Poll Tax - ed).
I'm not necessarily against ID cards, but I thought in Blair's Brave New World we were going to be honest about tax-and-spend. Did I miss something?