"I am now very uncertain of what my welcome would be should I happen to perform in either a Mudcat "singaround" (a word I hadn't encountered before arriving here) or its live equivalent anywhere in the UK."

Well, there's one way to be certain about what your welcome would be, should you join us at the Mudcat singaround, and that's to join us, and see. I've been to over 70 of them, and I have never found them to be anything other than welcoming. [And I'm not sure whether the UK reference was linked to the Mudcat singaround, but that singaround is hosted in California, and USians and UKians make up the largest cohorts of participants.]