That's not your ID number, that's your tax demand.

I would never like to imply that the accountants in the tax office are obsessive nitpickers and information gathereers. Far from it. They might audit me.

However, I was forced to ask some probing questions when I got my latest tax return, part of which read Your personal account number (which should be quoted in all correspondence) is 9JYHBG67FDRWW8MNQ10OYGA5B3X9LK*. That's a thirty-one digit number comprised of both random numbers and letters, so no chances of error in data entry there then.
It really makes me ask, though, just how many people they're expecting to get to pay tax. A bit of mental arithmetic suggests to me that they could cover ₁₀30¹⁶* people with a numbering system like that, and that's more people than there are particles than the observable universe. Add to that my National Insurance number (another 10-digit ID of both numbers and letters) which I also must quote in any correspondence, and suddenly there are more potential taxpayers in the system than there are electrons. To bring it home, that's about 100,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 possible combinations.
What makes it worse is that it suggests that there are ₁₀30¹⁶ people with my National Insurance number alone, and it rather feels from my tax demand that I'm making NI contributions for all of them as well as me.

But really, 41-digits of identification per person? Surely there is a simpler way to do this?


^{*Not the actual number quoted, but a fair representation.
*If I'm wrong, I'm sure one of you more number-oriented people out there will tell me.}