Friend worried sick but wants to put it right

[Mazin]

Your friend should contact HMRC directly to disclose the issue and seek guidance on rectifying it fully. Consider consulting a new tax advisor to ensure proper handling and rebuild trust.

[wamstax]

But it will depend on how much your friend's pre tax income is and the Plan under which the loans were issued as to what Student Loan Repayments will be collectible... you can see the basics here >>>> https://www.gov.uk/repaying-your-student-loan/what-you-pay