Might as well necro this thread!
I've just had a similar thing happen to a flight next October from Tokyo. I booked a pair of First tickets (A bucket) for the 30th October from Haneda, which appeared as a 4-class 777 - I've travelled on BA8 a few times before.
This afternoon I had an email saying there'd been a seat change... and I was now in Club World, 11A and 11B, on a D ticket. The original flight was showing as cancelled, albeit replaced with an identical 777 with the same flight times. Odd! The only difference was that (using Expert Flyer), the entire First cabin was blocked.
I emailed You First and it seems that from the winter timetable next year First is no longer being offered to either of the Tokyo airports!
They apologised for moving me to Club World, but there was no mention of a partial refund.
I've (perhaps cheekily) asked to be moved to the JAL flight instead, as that *does* have first class - and it has A bucket fares too. Of course, they're not exactly the same price that I paid... let's see what happens!