I would personally try to write a letter to Royal Brunei, explaining that the delay caused the OP to miss the flight he originally booked and ask for reimbursement of the new ticket (s)he had to buy and take it from there.
Thanks Nick. I've emailed Royal Brunei explaining the situation and asking for reimbursement of the new ticket but they've rejected this based on the fact that the new ticket wasn't part of a Royal Brunei ticket/fare and recommended that I seek compensation from the travel insurer.
My travel insurer rejected my claim and recommended I seek compensation from the airline.
Don't know what else I can do except keep pestering them both in the hope they offer something.
On the APD front, Expedia NZ have been hopeless in trying to get a refund for the APD and British Airways won't deal with me direct since I booked through a travel agent (Expedia).
Frustrating!