A visit to citizens advice for a chat with one of their advisers would probably be a good idea. Have you spoken to your Mortgage Company, they may be willing to help by extending the term of the loan, or allowing you to pay interest only for a period. Both these will reduce your payments at least for a while. You can reassure the Mtg Co. that as soon as you get yourself in a better position you will make overpayments.
What about the option of taking in a lodger if you have spare room, you can charge a rent of £4250 per annum without having to pay tax on it which would go a good way to meeting the loan payments.
Finally have you discussed the position with your ex, if this doesn't get sorted and they repossess they will chase her for any shortfall if she is still on the Mtg. and if you cannot pay and she may be willing to help to prevent this.