Just for information, I got downgraded on the DXB LGW leg of a BKK to LGW flight last month due to an equipment change. I filled in the online form to claim a refund and have received a refund of 75% of the pro-rata cost of the downgraded leg. I have to say I am happy with this outcome as I am not expecting to be compensated for any legs where I traveled in the class that I paid for.

Trotski