Thanks all....
I think I got lucky. I called the ICC and asked them to put us on the earlier flight in business on the Saturday. They explained that there was no award availability left in that class on that flight. I asked them as the 'agents' to call Thai yield control to ask for two seats allocation to be shifted to accommodate us as displaced passengers. Initially, they refused to do this and then once I had said that I would want to talk with 'Donnington' Pre Flight Support and then asked to speak with a supervisor, I was.... wait for it.... offered the flight that we wanted yet in FIRST class with only the additional taxes payable. The extra miles (and cash component) were waived.
What Anne Robinson would have called 'a result' back in the hay day of Watchdog!
As I say, I think I got lucky and they probably just wanted to get rid of a pain in the neck passenger.