120% mortgage - does that mean 120% of the value of the property now, or of the value when you took out the mortgage (which was probably higher)?
Do you want to keep the house, or are you willing to move and rent? If the latter, it is best to move before going bankrupt - get whatever funds you need by stopping paying the creditors (including the mortgage lender if necessary).
You certainly can go bankrupt while you still own the land, but the Official Receiver would take over your interest in it and the proceeds (when it sells) would go to his costs & then to the creditors. The OR's costs in bankruptcy are high and - if there are assets such as your land - will be paid from the proceeds before the creditors get any money.
If you want to avoid bankruptcy, you should certainly try to come to a payment arrangement with the unsecured creditors.
As suggested, ask to see a money adviser at the CAB. Alternatively, contact CCCS (see their website).