A few points:
When I said "first class passengers", I admit I'm not sure it it was incoming First Class from someone else, or Business Class passengers holding simply London to Berlin tickets.
I British Airways has a PRIORITY ORDER to reroute/rebook passengers on canceled flights, then they have an OBLIGATION to inform people, in advance, of this practice and of the order, BEFORE tickets are bought/redeemed. That is, had British Airways informed me, in advance, that traveling on an award ticket would make me LOW priority in "airport operations" situations, I may not have redeemed an award for that flight... as it may have been CRITICAL for me to make a particular flight, I may have PREFERRED to buy a revenue ticket to increase my PRIORITY level. The point is, British Airways kept that a secret, before, during and after the situation. No one REALLY knows what their hidden priority system is. THis is wrong, and is not fair.
I hardly think their agents at the airport have the ability to sort everyone's ticket type out, when determining priority... that is why the ORDER of check in seems to me to be the ONLY FAIR way of determining who should get PRIORITY to go on the first flight out with seats. It's very clear, and equitable to everyone.
I agree that First Class passengers should be entitled to more room, better food and more baggage allowance... but they should NOT have the right to go in front of OTHER passengers who may have needed to get to Berlin or anywhere else, JUST AS QUICKLY as a First Class passenger.
FINAL POINT: Order of check in is the ONLY fair way I can think of, to determine priority for rebooking on canceled flights.