Originally Posted by
corporate-wage-slave
For EC261, I personally regard it as a downgrade if BA don't provide you with an alternative, but BA tends to regard the downgrade provisions as only applying for last minute downgrades. There is no wording in the Regulation that supports this, but that's the way it goes. BA's own recalculation for the downgrade may - or may not - be fairly similar, and they may award some Avios for the inconvenience. But look at the main EC261 thread in the Dashboard and do your own calculation of the Mennens formula (see wiki).
I would also see this as a downgrade and am rather surprised by C-W-S's comment that BA tends to regard last minute changes as downgrades. If you booked First how could BA say that actually travelling in CW is not a downgrade? It doesn't really matter if the airfare you paid was a deal the point is you booked First so should really travel in First. BA should to my mind offer you a re-route in a First Cabin. The Club Suite seat and service is not the same as the First seat. If you were re-routed during IRROPS you could apply for Original Routing Credit which would award you the TP and Avios you would have received on your original booking so I would think this would be applicable here if you chose to accept the downgrade.
Definitely call YouFirst to discuss your options. (That is a distinguishing feature between the two cabins in itself, if you only booked CW you would not have access to YouFirst).