And a very relevant fact too: my starting point is that one of the world's largest airlines would rustle up another aircraft from their second largest hub. Actually, that is over-simplistic, there are no spare aircraft at LGW, short or long haul. This is a commercial decision by BA, who presumably calculated the need to pay a few EC261 claims off, rather than have a spare bit of kit in LGW. So unless there is some very good other explanation (which I can't even find a hypothetic example) then I'd pushing strongly for payment in full.