All you have to do is work out what you can afford to pay this creditor - it may not be as much as they would like but if you work out a budget sheet it will show what you can afford. All creditors should be treated fairly so they should be paid on a pro-rata basis i.e. in proportion to what they are owed. Put simply if you owe £10,000 to three creditors - £5,000 to one; £3,000 to another and £2,000 to the third and you have £100 left after paying all your prioirity bills like rent, housekeeping, travel, clothes etc, then you would pay them £50, £30 and £20.
Contact one of the free debt advice agencies like NDL or , CCCS or FCL/Payplan and let one of their advisers go through a financial statement with you. Their advice is free, totally confidential and implies no obligation to take the advice. Give them a ring - I am sure you will see there is some light at the end of the tunnel.