Your case is unfortunate and complicated by the fact that you aren't here to sort it out?
As far as I know and the way the rules are at the moment, if you walk away from this place, it will sprout some legs and follow you (and your mum if she is still involved). Abandoning houses in this country doesn't really work like it does in the US. You and anyone else who has a stake the property will be pursued for the difference between the amount borrowed and any knock-down sale price secured for it should your lender take possession.
It's time to organise some sort of correspondence with the lender to outline the predicament. The fact that you tell them that you are in financial difficulties does not mean that they instantly move to repossess. It's in their interests to help you keep paying something towards the mortgage, either by restructuring the loan or accepting reduced payments.
If you demonstrate that you're serious about sorting it out, the lender will take you seriously. If you welch out, they'll give up quickly and there'll be a court hearing and you'll lose the apartment as well.