Senior exec. in the tech industry here:
In a nutshell, nobody in industry cares about A-levels one you've been to a university. So pick whichever ones unis prefer.
In terms of degrees: yes, computer science is an obvious choice. Or any computing related engineering degree, too. I've also known some stellar architects with degrees in physics, mathematics and even one with an MSc in chemistry. I'm not personally much of a fan of "soft tech" degrees such as "Web Computing" and that kind of thing. Not saying they categorically can't produce good grads, just that - on average and in my limited personal experience only - they tend to produce fewer than, say, computer science, software engineering or similar, more core tech degree courses.
Then, after graduation, basically you don't normally get to be an architect straight away. A typical career path would be something along the lines of developer > development team lead > technical architect > enterprise architect. Architecture tends to require experience that you'll usually get by designing and implementing systems from scratch for a while.
Having said that, a good architect is a gem and a great architect people like myself would be willingvto spend their weight in gold on. It's a great career choice. Just not an instant satisfaction one.