Working as a contractor for a US company

Hello, I will be starting my masters course in the UK this fall. I have working for a US employer since 3 years as a contractor although full time. Contractor helps them with taxes that's why the term. Would it be possible to continue working in a similar manner during the course. Ofcourse following the time limit of 20 hours a week. I provide my employer with the invoice for the same. Any help would be greatly appreciated. Thanks

There is an existing topic about this:
uk-tier-4-student-visas/working-on-a-st ... 19537.html