My dropping out of university was held against me during my first medicine application. I only managed 2 interviews (both very late), and no matter how well I explained my reasoning at interview, they kept hammering at it. Ultimately, I ended up spending over half of each interview defending my withdrawal and trying to steer it towards more positive reflections.
Medical Schools have a huge number of applicants every year. They will use any excuse possible to cut down the number of people they have to consider, and some medical schools may not like your cloudy academic history. If you do get to interview, you'll most likely be doing so in an atmosphere where you're constantly having to tiptoe around the negatives of it. And if you end up being a borderline candidate, chances are they'll take the applicant with the clean history over you. I'm afraid that's the reality of it.
That's not to say you can't drop out and get into medicine. Plenty have, but you will be at a disadvantage. My advice would be this:
(1) If you really don't like your current degree and don't feel like you have the motivation to stick it out and get a 2:1, then quit and spend as much time as possible preparing your application for medicine. If you feel like you can tough it out, stick with it and apply later.
(2) When you do apply, make sure you pick your universities wisely. This is pretty much universal for everyone who applies to medicine, but it'll be particularly important for you. E-mail any medical schools you're considering and ask them if anything in your application might negatively affect your likelihood of being accepted.
I got rejected after I'd dropped out, did another course, applied as a graduate this year, and now have 3 offers (with another withdrawn).