Your main problem is your husband. He had got you into a situation where you are behind with your mortgage payments and he has run up a substantial personal debt. What has this money been spent on? Gambling seems an obvious explanation, although it may be an expensive taste in wine, cars, holidays, or clothes among other things.
No matter what his weakness, until that is faced up to and dealt with, there is no satisfactory way forward. I think you also need to speak to a lawyer about your own financial situation. Whatever happens to the pair of you, you must make sure that your own financial interests are protected so that if your husband continues to rack up debt, you do not end up pennyless on the streets.
the enxt question is what is your house worth? You say you have a £120,000 mortgage. Is the house worth £200,000 or, for example £450,000.
In the first case the mortgage lender may well press for a quick sale, regardless of the houses real worth because they will want to get as much of their money back as possible before it exceeds the value of the house. In the second case, they may well be prepared to let you wait out the current lull in house sales end and the market picks up.
Our house is for sale at the moment - and has been for 6 months. Our house is considered highly desireable, but quite, simply, at the moment there are no buyers in the market. The election and the promise of a drop in interest rates in the next few months mean that buyers are holding back. Lowering the price will not help you - in fact it does you a disservice. There are no buyers around and dropping the price will not conjure them up. You need to sit down with your mortgage lender and discuss the best way forward.
However the first thing you need to do is deal with the cause of your husbands debt problems. Until that happens, if you get out of this problem his debts are only going to cause you more problems and having defaulted on this mortgage, you are going to find it very difficult to get another.