British Airways has a few different flight attendant contracts. One of those contracts is for their “mixed fleet” crews, which are their relatively newly hired flight attendants.
As you may remember a few years back, British Airways flight attendants went on strike because they couldn’t agree with management on contract terms, and British Airways threatened that if they didn’t have more reasonable terms then they’d stop hiring flight attendants under their contracts.
The flight attendants didn’t give in, so what British Airways did is start hiring “mixed fleet” flight attendants, which operate select shorthaul and longhaul flights. They’re paid significantly less, typically stay at worse hotels, and have shorter turnarounds (typically only one night).