Join Date: May 2000
Location: Houston, TX, USA
Programs: UA Platinum, AA Lifetime Platinum, DL Platinum, Honors Diamond, Bonvoy Ambassador, Hertz Platinum
Posts: 8,179
I suspect the airline pings the UK ETA system automatically with the passenger's passport information when a BP is issued. If you don't have an ETA, you don't get a BP. So, there's nothing to present to the airline as the passenger.