I don’t think there’s any such requirement – I’ve been to places where there were no veggie options at all (most recently a pub in Norwich). It’s just that in this day and age, there are enough vegetarians around that you’re going to lose business if you don’t offer anything they can eat (because groups that include a vegetarian won’t visit).
I’ve had linda mccartney sausage rolls. They’re pretty good, but not as good as the real thing imo. I used to have a mild addiction to the popty quorn cornish pasty – those things were so good! Might have to have one (or several) when I’m back in town for JTA’s graduation.