I am not a lawyer and I have never been to the UK so you'd be a fool to rely on my advice.
You should be able to state that you took an exam, were asked such and such questions, and provided such and such answers. You should be able to also say which ones were marked right and which were marked wrong. I'm aware that "fair use" doesn't exist as such in the UK, but I believe there's a similar concept there that should cover this reasonable situation.
Now it's entirely possible that a condition of attending the University was agreeing not to do what you're proposing. If that's the case and the agreement is legally valid, then you might be in breach of the agreement and the University could have remedies under the agreement and/or the law. For instance, your University might have an academic honesty policy that prevents you from doing this and there may be penalties for violating it, likely up to and including expulsion. I somewhat doubt that they'd try to come after you for more than that but I'd read the policies.