I returned from Delhi last week and travel there and back from the UK 2/3 times a year. I have never been able to print a boarding card in advance. I show a printout of my itinerary to the officer on the door (along with passport). I have seen others show the flight booking on the app to the officer.
Hope this helps.
Last edited by GandT; Sep 25, 2019 at 3:22 am