Hi mate, I am a graphic designer by trade.
Graphic design and automotive design are very different things. You will need to design what area you need to go into.
If design, then I would suggest you attend a National diploma course at college. If you have 4 or more GCSE grades C and above then you can get straight onto a National Diploma B-tec course.
If not, then you will need to do a foundation B-tec course which will be one year, then onto the National 2 year.
This will give you a more directed education into design and make you more focused.
After this you will be 18-19 years old and will be looking at uni - or into the workplace.
Now, me personally I would get into the work place, the wages will be poor but you will gain masses of usable experience. Don't stay in one place to long, get ayear done in one place and look to move up into a better position and a better firm (or the same if it is a good one).
I was nervous about going to college but it was the best move i ever made, firstly you are treated like an adult and act more mature due to this.
Secondly, you are surrounded by people with the same interest as you and will make new mates etc.
thirdly, there are far better levels of equipment and specialist teaching at college.
Graphic design is a good line of work, but is not very glamerous, lots of mundain jobs with a few nice tasty bits of design thrown in.
One thing I would say is that many of the uni students i come across have very little or no knowledge of print and this is a huge part of design and it is this knowledge that can be a huge plus in an interview.
If you have any questions let me know.
Matt