Yes. Casual earnings in Other Income (Box 16 on the basic return). I've done a post on the Etsy Burning Issues thread about it here & added a paragraph to TSCB 1: When will HMRC be interested in me?
But it comes with an enormously huge and giant health warning - don't do it just to avoid the hassle of the self-employment registration & annual tax return. And certainly don't say 'oh but this blog on the internet said it was ok for me to do it' - I didn't at all! You have to take responsibility for your own tax affairs, all I'm doing is helping people find the information they need to make an informed decision - you need to read up HMRC guidance to decide what's legal and appropriate for your personal circumstances, not just read what I'm highlighting and hope it applies!
I will eventually do a post on it, towards the end of this current series. But am just bringing it to your attention in case it applies to you so you know about it before the 31 January deadline at the end of this week.