I'm not sure about undergraduate degrees, but I am currently looking into appyling for a postgraduate degree, hopefully starting after I graduate from my current university in 2019.
For the postgraduate degree, at least, they do look for quite a lot of experience. I've heard other applicants saying that the universities ask for shadowing with a speech therapist (which is very difficult to get by the way, you basically have to email private speech therapists because there's just no way that you're going to get anywhere through the NHS), experience with children, experience with adults who have autism, or adults who have had strokes, and also experience with children who have autism or similar special needs would also make your application stronger. And maybe also experience with elderly people who have dementia, or similar diseases. And I also emailed Queen Margaret University about it as well, and they said experience with general healthcare would also be helpful, so you might want to look for some volunteer work in a hospital.
But yeah, you do need quite a lot of experience, I think. I've been volunteering with Girlguiding for three years, and I'm still looking for more volunteer work to make my application stronger, so yeah.