I really don't get what you brits are so afraid of. Yeah I have a California ID and a federal Social Security number. Both these things are essentially required. However, when has either one been an invasion of privacy? Can anybody give me one example? One?
If it's more than that, then speak up and tell us all why it will deny you all privacy. Go ahead.
Because in order to be reliable as an identifier, that card has to be passed through a reader that will obtain biometric details from a central database and match them against encryption data on the chip. Thus, those accesses can quite feasibly be stored and tracked and used to identify every service you use that requires the ID card - be it opening a bank account, having an operation on the NHS, travelling on the train or plane, etc. Furthermore, the Id database will act to tie in all sorts of previously discrete record systems; such as your aforementioned NHS record, when previously this information was seperate and required clear legal authorisation for access. Also, you will not be allowed to know who is accessing your personal data (the Data Protection Act can bar people from knowing what is stored upon them if it is deemed in the national interest).
Finally, these cards are a colossal waste of money and will be wholly ineffective for any purpose beyond tying together all your personal records. In terms of specific security issues, not only does the government admit Id cards could not have stopped the 7/7 bombings, previous examples in Northern Ireland have shown ID cards reduce diligence in inspecting identity (a photocard ID was introduced there; it became the situation that posession of such an ID was enough to grant checkpoint access, rather than close examination - simple wave and go, same as you get from people pretending to be gas inspectors or FBI agents with false IDs) and rather act to stimulate forgery due to the placing of all ID eggs in the card basket (so to speak).
So we have a vast waste of money - taxpayer money - on a useless system whose only value is to store information about us and let the government access it for any purpose we deem fit, without us having a right to know what that purpose is if the government doesn't want us to.