Recently travelled LHR-MAD- South America all on a single BA ticket, the Madrid onward being on Iberia metal.

I’d uploaded my covid docs to both BA and Iberia but never received any verification from either.

When I checked in at LHR with BA I couldn’t get a boarding pass for the Madrid onward section. The staff said, as they didn’t do South America, they had no idea if my docs were in order and thus it was up to Iberia to decide to carry me or not. My bags they were happy to tag for my final domestic connection.

As it turned out despite an outward delay causing a tight connection everything was fine , transfer desk in Madrid T4S issued my pass without looking at anything but the question gnawed away as to what would have happed if it had gone wrong and they’d decided I didn’t have the right paperwork.

Would it be up to BA to return me to the U.K. or is it Iberia or would I have to sort myself out.

equally with a potential missed connection and Spain issuing “transit” approvals what happens these days 🤷‍♂️.