I did zero work (literally revised about 10 mins before each exam) at GCSE, got 4 A*s/4 As/1 B, strolled into AS expecting it to be just a bit harder, and I'm failing. To be honest I think it's not that difficult if you put actual effort in, but if you - like me - don't care in the slightest, lose all your notes, never do homework and never revise, it's pretty difficult. Maths in particular is making me lose the will to live. I always enjoyed it but was never overly good at it; however, after a lot of deliberation I decided to go for it and well, biggest mistake of my life. But yeah, if you try hard and don't make the mistake of assuming you can cope doing no work, I think A-levels are manageable.