Is it possible to apply to courses in clearing as a student who's already enrolled at another university? Just curious as I'm not sure about continuing with what I'm on currently.
But you'll need a UCAS application to use clearing. You should submit that ASAP as it needs to include a PS and reference (ideally from your current tutor).
You need to think about if you want to restart from first year or apply for entry into 2nd year. Technically clearing is only to match students to courses with first year spaces so there may be fewer options available for 2nd year entry.
Can you switch to another subject at the Uni where you are now - you can usually do this internally without bothering with UCAS/Clearing etc - just contact the Dept where you want to study asap.