Originally Posted by
cs19
For BA flights intra-europe booked into D-class (Club Europe) you cannot assign seats early unless you have BAEC status.
That's not entirely true. You'll only need to be at least OW Sapphire to assign seats on BA flights. The OP's AA EXP status will suffice for this purpose.
And it actually applies not only to intra-Europe but ALL BA flights booked into discount classes, ie anything that's not F/J/W/Y.