Just to add, in case anyone else is reading this, "no checked baggage!"

BA flights land/depart at T4S and you have to take a fairly long walk/train to T4 to collect baggage & re-check it.

I did this recently (but made sure I didn't take the immediate return flight) and it was an annoyance.

Also, in case people are still thinking about doing this, as mentioned above make sure you don't inadvertently mix up codeshare (Iberia) flights with the BA ones as Iberia uses the main terminal, not T4S.