Sounds like there is €70k to €100k negative equity.
Can your rent the house? The interest element of the repayment on €260k at 3% is €8,000. So if you can rent it out for more than this you will be making a profit, although you may have to pay tax.
The capital element of the repayment will go towards reducing the outstanding mortgage and maybe you will have paid off the negative equity after 10 years or so.
But you should tell the bank that you are moving to England. You don't want to go bankrupt and you want to pay your debts. But if you pay off the proceeds, they will have one less loss making tracker. Will they accept the proceeds in full and final settlement?
Try it and see how you get on.