Hey!
Not a silly question at all!
In short, yes, advising at your university legal clinic could count as a position of responsibility, and it is also fine to refer to it in both sections if it is one of your strongest points.
A good way to approach it is to use each section for different purpose. In the work experience section, you can keep it factual and concise (e.g. what the clinic is, your role, the type of work you did). Then, in the "interests / activities and positions of responsibility" question (which is usually longer) you can go into more depth about the responsibility element: client contact, taking ownership of matters, exercising judgment, teamwork, impact, skills developed, etc. That way, you aren't repeating yourself, just building on it!
I'd say that legal clinics are generally viewed very positively by firms, and they're likely to be more relevant than positions from Year 11 (although you can definitely still include these if relevant in some way).
It's usually fine if this slightly overlaps with other sections of your application - the graduate recruitment team expect some crossover, especially when an experience is particularly strong. The key is to use the space to emphasise the responsibility and skills involved, as that is how you will demonstrate how it is a position of responsibility (and also link to the firm / role!).
I hope that helps!
