British Gas's programmers don't believe that a surname can be only a single character.
Their customer service agents worked around this by adding a parenthetical note to my record.
The result is hilarious postal mail that tries to reassure me that my surname really is what it is:
EDIT: Well this blew up. FAQ etc. at https://danq.me/it-is-only-q
It was interesting to read on your site (at https://danq.me/2007/03/08/q/) that you need to have (at least) two names in the UK. Here in the U.S., I have a friend who is legally mononymic. Like you, they have had a hell of a time convincing people that their single name is real, legal, and accurate, not a stage name or nickname.
@funcrunch I might have been misinformed about that, and I'm currently working with somebody to help test the case. It certainly seems to be required that two names are required when registering a birth, but it seems perfectly feasible (and has been done) to CHANGE your name to a mononym. Although yes: it causes hell with computer systems including government ones!