I sadly concur, as someone who did fine at Computing A-Level with no work, found Further Maths difficult and was lucky to get a B with extra tuition and some juggling of module results to maximise my two final grades, and dropped out of a CS degree.

I liked coding for fun but really had almost no idea what CS was when I applied. So maybe the US system would have been better for me in that I could have dipped into a bunch of 101 courses and changed my major.

In the UK system, most people don't go to other subjects' lectures and if you don't like what you're doing, you have to apply from scratch. There's usually no way to change course at the same university or even get any kind of help or advice about finding an alternative elsewhere.

One of these years I'll work out what I should have studied and do that instead... actually, I probably won't, now it costs £30k+. I'm glad there are MOOCs so I can satisfy my urge to sign up for random things, watch one week's worth of lessons, and then never go back again, all for free.