Looking at the requirements for tier 3 interviews, I think anyone who is in that category and doesn't have a suitable device needs to be thinking about how to do it now, rather than waiting until they know they have an interview. I noted that there was a comment on the info page that they had already been in touch with some schools to check / assist. If you haven't got a touch screen + stylus, and can't get access to one at your school / former school then I would think the university will have some ideas how to help. I couldn't see obviously where you would ask though. Very glad my daughter has applied for a tier 1 subject ...
Earlier in the term when my daughter was doing choir auditions they made it very clear that they wanted to be contacted by anyone who had difficulties with the requirements (eg video with an accompanist), in order to find a workable solution.