Thanks for the link Sam. However the issue I am facing is that my broker is not yet willing to mark the stock to zero, even though the independent valuer has deemed that shareholders will receive no compensation from the UK government.
Sounds like it's similar to the trading being halted pending news or investigation. You're just stuck in that case. Your broker should work with you and help you, but if it can't be closed there's not a lot they can do. They should forgive interest payments though.