Difference between gcse and a level

I prefer a levels because there's less subjects

I probably have a warped view since I'm doing 2 and a half a levels

Yes there is less subjects to do at A Level, but I did 4 and it felt like 8. I guess it also depends on what A levels you are doing. I am at med school now and I did some of the hardest A Levels you can do to get into Uni and one of the hardest boards OCR, not to mention the grades you needed to get in. I did Biology, Chemistry, Maths and Music.
So A Levels was no fun, I had to really work hard to get the 2 A*s and 2 A's.

Personally I really like ocr. I also respect you for taking music

Difference:
GCSEs are irrelevant, A-levels are more concerned

Trust me, GCSE's are relevant, as firstly, you needed to obtain a certain grade, to be able to do the equivalent A Level and on some courses at University like Medicine and Engineering, the amount of GCSE's you had and the grades attached to them were part of the criteria for selection for interview or an offer. For example, one of the criterias just to be selected for interview to study the Medicine (A100) undergrad course at Cardiff University, was your best 9 GCSE's. An A* or a 9 at GCSE was equivalent to 3 points, an A or 8 & 7 was 2 points and a B or 6 was 1 point, which means your maximum total with your best 9 GCSE's would be 27. Even if you took 12 GCSE's, they only required your best 9. And to get an interview, you basically had to score 24 or more points.
So in some cases GCSE's are more than relevant, they are crucial.

maybe for medicine and oxbridge but not for engineering

The point is GCSEs are relevant, NOT irrelevant. And yes, many courses including Engineering require some GCSE's, whether it's Sciences for some science courses, maths for science, engineering and mathematical courses. Enlish language at GCSE is required on a lot of courses also. A friend of mine didn't get into UCL this year to do a psychology course, because she didn't have at least a B in her GCSE English. She had the grades at A Level, but they still required the B in GCSE English. So yes GCSE's are relevant. And trust me, some may not stipulate it, in their entry requirement, but they would expect it.
Courses like Aeronautical Enginering and Civil Enginering do require a minimum standard of GCSE's.
And it goes without saying, some A Levels cannot be undertaken, without the requisite GCSEs.

Ohhhhh, ok! GCSEs are not irrelevant but as long as you get grade 6s or above for english, science and maths youre fine. Ace your A levels and they would cover for your GCSEs. Easy!

Except in Oxbridge and Medicine of course, which are determined by how many A*s you have at GCSE. Determined, may be the wrong word (I can't think of another right now), but even if they don't actually stipulate how many you need, except for Cardiff, when you look at the statistics of grades of those lucky enough to get offers and who ultimately get in, the average is roughly 9 or 10 A*s and above.
I applied to Jesus College Cambridge last year and was rejected post interview. When I looked at the stats of the offer holders at Jesus College for medicine on the FOI, the average offer holder had 10+ A*s at GCSE. Incidentally, the average applicant invited for interview had 6+ A*s at GCSE.
A person on TSR was told in their feedback from a rejection post interview at Cambridge, that one of the reasons was because their GCSE's were not quite good enough, even though they were good enough to get the interview in the first place.
So this just goes to show, GCSE's are relevant and important, even if they are not stipulated as a requirement.