Just made two phone calls to Qatar in Doha. As regards possible overbooking of my flight from Doha to Bangkok, there is one seat in Business still unsold on my flight, and 4 or 5 unsold on the flight that leaves just 15 minutes later, so that panic is over.

Regarding my involuntary downgrade, I was told that as I have already been provided with an alternative flight, the matter of any possible compensation must be handled by Qatar Customer Care, who, I was told, cannot be contacted by phone. I called back about 20 minutes later (remembering the souk advice from MSM2000) and was told exactly the same, so I shall be sending them an email, asking if one of the two flights I already have booked for the first half of next year can be upgraded to First on that same leg that has been downgraded this time. To me this seems eminently fair and reasonable, but whether Qatar share that view is another matter. I will report back on what they say.