If you have outstanding debt from building society handed keys back 10 years ago have not heard from them till today had letter for balance what if I offered them a percentage as I have not got much money

You can offer but it's up to them to accept or not.

Worth a try but you do owe the money.

The issue of "turning over the keys" is you could owe almost as much after it is all done. There is all the late fees, cost of sale, perhaps advertising or auction.

So they can go to court and get a judgement for the amount,

So while they may accept an offer it would have to be enough to be considered in good faith.

If they say you owe 50,000 and you offer 1000, it is doubtful they will take it seriously