The surplus is after your normal household expenses are taken into account. It does not include debt payments.
Bear in mind that the debt also has to be below £15k with no assets. You cannot own your own house and cannot have anything else worth more than £300, including a car.
The friend in my adversity I shall always cherish most. I can better trust those who helped to relieve the gloom of my dark hours than those who are so ready to enjoy with me the sunshine of my prosperity. – Ulysses S. Grant