Any other art school graduates or working art people here? There's a lot of talk here from people who have no or very little art school experience. It's easy to shit on art schools to make yourselves feel better for not going to them, but I'm also not seeing these art school detractors demonstrating that they have the skill or experience that proves that art school has no value compared to internet-driven self-teaching.

OP, the biggest pieces of advice I have about art school is that 1) don't go into debt over it and 2) the experience is what you make of it. Art as field doesn't pay well enough to justify the cost of a private art school tuition (in the US anyway) but since you said that you'll have scholarships and you're in the UK, the first point is not an issue. The second is that based on experience and observation from getting two college degrees, one in an academic field, and another in design. Anything you do and your subsequent success will depend on how you handle the educational opportunities you get while in school. No one will sit you down and help you as an individual student. It's on you to hunt down the resources and apply yourself. It's very easy to go through school, going through the motions, doing assignments without really thinking about them, not following up on internships and professor office hours, and find yourself at the end of 4 years with no idea what to do in the real world, and blame the university for it. The people who succeed are the people who take responsibility for their own education and actively pursue their careers.

It's hard to say if you have a chance to get into a decent art school with no other information. Everyone can improve in the course of a year, but it's a rare person who can go from zero to art school on their own. In the US, every major art school I know of offers summer prep courses and portfolio development courses for high school students. You should check if that's an option for you.

The number of hours you spend working is not as important as how you work, which is why I recommend getting some formal instruction before committing so much energy to it. You don't want to re-enforce bad habits or waste time. I'm sorry I can't be more specific without seeing your work samples.

In North American, there is an organization called Portfolio Days which hosts events with admissions representatives from all the big art schools in major cities, where students go to get evaluated. I don't know if there is a similar program in the UK, but the best information you can get about applying is to contact as many art schools as you can travel to and ask questions from the admissions representatives. Hop on google and look for independent schools as well as programs within larger schools.

There are indeed many good art and design schools in the UK. Central Saint Martins and something else in London are the only one that pop up in my head at the moment but I do recall seeing plenty of UK schools whenever I looked at lists of notable international programs. (It's been a while since I've had to look and my memory for names is crap.) In the US, any school worth its salt will require a portfolio for acceptance, I imagine it's the same in the UK. Here, there are a good number of schools with excellent graduate art program and terrible undergraduate programs, so be aware of that as well.