Tutor forums are voluntary, in my experience no one uses them anyway.
TMAs are graded, and go towards your final grade.
Not only that, but they further educate you on the subject so you have a better chance of passing your exams. It's also a chance for your tutor/s to give you feedback and help you in areas you're struggling on.
If you don't submit TMAs, you fail them, and will probably fail your module altogether / get an awfully low mark.
I don't think the fact you failed all your TMAs is going to look good on your application to a brick uni haha
Edit: Also, your tutor is going to be so confused as to why you are not completing TMAs. This will cause a lot of hassle and your reason might not seem good enough to them or the head of department.