WAW - Fast track not available for Gold travelling in EuroTraveller.
Automated gate at fast track channel rejected mobile BP and when I asked the guy on duty he pointed to a laminated card that showed only a few airlines had access (no sign of BA). Not sure if it would work for BA if travelling in Club Europe. Normal security line was not too bad (longer wait at the Non-Schengen passport control)
there's no fast track for BA customers at WAW, it has been like that since January 2020, when they've outsourced managing fast track to the external company - instead of working out eligibility from status encoded in your boarding pass, they require airlines to sign up a separate agreement and make changes to boarding passes - many airlines chose not do it. Not a big loss for BA customers - regular security next to BA check-ins is usually not busy and it's much closer to the Fantazja lounge...
Fun fact is that old "Gold track" sign is still by the entrance door to the terminal and have many airlines listed there (including BA) that are no longer eligible to use it...