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.
Hi, what happens if don't take part in tutor forums and chose not to submit TMA assignment. I just wanted to study and take the final exam. My reason's been this is not the course I wanted to do, but a short cut into the physical uni. Please, a polite answer will be appreciated. Thanks
By completing the TMA's it will really help your understanding of the course and also help you develop a relationship with your tutor so that if you require help with exam revision they will be more inclined to help you. Sometimes if you are on a grade boundary for your final exam your OCAS (overall continuous assessment score) can be used to help determine your final grade, having a high OCAS can push you into the grade boundary above, a low one will obviously drop you below.
In the end it is up to you, there isn't really a short cut into uni. But unless the new uni just wants to see that you have studied the course and don't care about your grade then you could be harming your chances by not participating fully and giving yourself the best opportunity to do well on this course.