What basis would you have for suing? You agreed to pay the extra tuition to re-do the project, and got it re-graded. Unless you feel that the grading was done unfairly all 3 times and you should've gotten a pass (without requiring a re-grade/extra £10,000), but even then, you paid the tuition for the grade. It's not like you get to not pay back student loans if you fail a semester.
I also don't see how you could get £30,000 out of the school, either, if tuition is £10,000. They're certainly not going to reimburse you for your living expenses while waiting on a re-grade that you signed up for.
So...color me confused.