Although compulsory would it actually be possible to exist without one?
This will depend on what scenarios one will be required and if it would be possible to avoid such situations. It will certainly be required in most situations involving a government body such as a claim for benefits or treatment on the National Health Service. In addition if the ID card replaces passports and driving licences then any situation that would require either of those documents also.
I believe it is possible to avoid all of the situations just outlined as I have myself done so without really trying for the last couple of years. I don't claim any social security benefits, haven't been to the doctors or hospital in years and cannot remember the last time I showed my driving licence to anyone. The only exception is my passport as I have travelled recently.
I should point out that if the scheme were to become compulsory then failure to acquire an identity card would be a crime that would be punishable by a fine of up to £2500.
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