Negative equity - negotiating with lender

SherlockNomes

Does anyone have any experience of marketing their negative equity property in Northern Ireland and then negotiating with the lender to do a deal on the shortfall? If so, which lender? This is something I am considering doing to address c.£70k negative equity - I know lenders do it behind closed doors, but want to avoid middlemen/negative equity companies (plus their hefty fees) and negotiate directly.

All experience gratefully received, thank you