Northern Rock do accept a lot of IVAs, but they do have a strict acceptance policy and if they feel that there is an alternative solution which offers a better return - such as a DMP - then they may well reject.
Their insolvency team reviews all IVA proposals thoroughly, and they will take special circumstances into account, such as the effect on your employment, the events which have led to insolvency, and the amount you can afford to pay back, but they do not take kindly to applications where they feel the debtor is deliberately attempting to write off debt under a five year repayment plan, whereas it could be paid in full with some longer effort.
Regards, Melanie Giles, Insolvency Practitioner