Definitely try talking to the bank and coming to some arrangement.
The problem is the banks are not very commercial and trying to engage them in conversation is an uphill battle. If you don't speak the lingo then find someone who can.
I know someone who had a mortage that exceeded value of the property but she was able to agree with the bank to sell and they converted shortfall into personal loan at existing mortgage rate. This woman did not just want to walk away and she is now paying off the loan.
Maybe first of all find out if the property is at all saleable and then at what price - that will help discussions at least.
It's quite easy to sit here in Spain and file claims into UK courts. I do it and the UK courts communicate here with me in Spain. Spanish lawyers are shocked at the efficiency and the speed at which I am able to obtain judgment. I have had only one small challenge on jurisdiction.
Up until now Spanish banks have not done a great deal on chasing debt in the UK and one of the problems is they have bad records and can't find people in the UK. The other problem is the arrogance of their legal department and they will not use outsiders who know the system. And another problem is people with mortgage problems in Spain usually have similar problems in the UK so for now sit back and wait.
I have done work for one Spanish bank (2 cases) and it was NOT easy working with them - basically a lot of internal politics. If I had the time I would like to talk to other Spanish banks about UK debt recovery.
So only as a last resort throw back the keys and run especially if there is positive net worth in UK.