I can't recall any rules against it here.
Aside from rules specific to this site, there's no laws on writing about incest in fiction that I can say I've ever read about.
I think I heard there's a rule against it on Patreon or something...?
There is no specific legislation which bans the writing of incest in fiction in any of the UK's jurisdictions. The closest thing you could get would be the
You must be registered to see the links
.
It is worth noting that the last time the UK Government attempted to prosecute someone with this legislation was when a fella wrote some guro fiction about a famous girl band. (
You must be registered to see the links
) The argument being made by the prosecution was not about the content of the fiction, but rather that young fans of the girl band could accidentally access the story. The charges were dropped after it was proven the fella who wrote the story had significantly obscured his work from children so that it wasn't easy to find.
Patreon has its own site rule against incest pornogrpahy, and other "taboo" fetishes.
It's important to note that Patreon's rules around pornographic content are heavily influenced by the payment processing companies which Patreon uses, moreso than Patreon itself. This includes Visa, Mastercard etc.