I flew into the UK yesterday and neither the airline's online or check-in stages advertised the fact the PLF was necessary in an obvious way. It was rather like all the small print at the bottom of the screen at the end of a TV commercial, legally there, but somehow not.
I was surprised that they needed SO much information on the online form, it went on and on. It could have been half the length and been effective. A man within earshot was pleading with the gate staff to provide a way for him to complete the form as someone who didn't own a smartphone! He was getting very stressed and the staff were unable to help, it just didn't compute.....