Re: Genuine Question
A social security number, as the article points out, is kind of a universal ID number assigned to every citizen at birth, or when they're granted citizenship in terms of immigrants. It was never really intended to be used that way, but since when has that ever stopped us (happy coincidence)? If you want to buy a car, get a loan for a house, get a credit card, or a number of other things, you provide that number as a means of proving your citizenship and thus eligibility. Technically it's just meant for when you reach retirement age in the US you get a small pittance from the govt. Not really enough to live off of anymore, but a pittance.
I assume in the UK you have some kind of unique ID for tax purposes, so it'd be like that.
People can be given new numbers, but since it's generally so intertwined with so many other systems it's not as easy as it may seem. You have to change hundreds, maybe thousands, of individual records across hundreds, maybe thousands, of databases which are not necessarily connected in any way. And if the social security administration just sent out some kind of missive saying this is the new number for Joe Blow, you can bet ne'er do-wells all over would be looking to intercept those.