Apart from the fact that most British citizens are against any form of ID cards, this will not stop illegal immigrants crossing the channel in small boats. They certainly wouldn't be turned back and most people view this as the Labour government moving towards authoritarianism, although I see that as a tad exaggerated.
I don't much like having an ID card, but I've got used to it and see the pros and cons. Yet, that doesn't stop illegal immigrants entering Argentina does it?