After submitting the essays written for post-graduate modules and after they were graded, can we post them on platforms such as academia.edu or researchgate.net? Are they under University's copyright or our intellectual property? I would like to help out other students by sharing the essays, but I am in a dilemma.

Let me know your thoughts.

Talk with your supervisor. I don't think the university will have any copyright claim though you would be expected to mention your affiliation. The bigger issue might be that once you publish it you can't copy it in further work. If you want to develop those essays later into more rigorous academic research you might find self plagiarism issues which can be an utter pain.

It's actually the case the vast majority of Universities have clauses that give them IP ownership of all student work.

This is not so they can pettily sue random students for posting essays online, though, it's to lazily blanket cover situations where e.g. a student might work on a dissertation with a supervisor then run off to industry with their coveted £10m of IP.

The awkward thing is they could *possibly* at a real stretch litigate you for doing this. They will not care, notice, or bother, though. It's the same with academics sticking the many, many pre-prints on researchgate etc. that could *probably* be taken to court *somewhere* but no publisher in their right mind would bother.