A consortium led by JC Flowers, the US private equity group, has rejected an attempt by Sallie Mae to renegotiate its collapsed buy-out deal, sending the student lender’s shares sharply lower and reducing the likelihood that a legal dispute between the sides will be settled.

In a statement on Wednesday, Sallie Mae said that over the past two months it had held discussions with the JC Flowers group in which it proposed to change the terms of the deal and allow the buyers fresh access to its books.