CSLM11014 | Borrowers questions and answers: contents making payments through my employer: contents: I am subject to Off Payroll Working rules – are my Student Loan payments deducted by the fee-payer
From HM Revenue & Customs · Collection of Student Loans Manual
No, the fee-payer is not responsible for deducting student or postgraduate loan repayments for workers engaged through their own companies. You will need to make your student loan repayments through Self-Assessment. You are responsible for registering for Self-Assessment. In some cases, you may be automatically registered.
You can find more about off payroll working on gov.uk.