BA appear to have sub-contracted some of their London Heathrow to Madrid flights to Iberia. Normally, BA tell passengers when they make this sort of change, not least because the service between the two carriers is different.
I found out when I was checking my flights for a trip next month and noticed:
Clicking in to the seat chart, it was clear it was an Iberia plane:
The A320 doesn’t have 1D or 1F to allow for a closet I think.
Anyway, it might worth checking if you think you’re flying BA to or from Madrid.