This is one of the big events that has now happened at 3 USA airports, JFK, LAX (and I can't recall the third one! SFO?); it is also about to come to LHR and T5 in particular. So in the USA already the CBP are populating the gates with information. So the gates know who you are from your biometrics. I don't think there has been full ministerial sign off for exactly that process in the UK yet, there are any amount of privacy issues involved, but I imagine BA could get regular travellers to sign off a one-off data capture exercise. For the time being, when leaving the USA the system will know who you are, when leaving the UK then there is a likely to be a short-term data capture at check-in - by self service kiosk for most - and then the rest of the scans at security, the lounge, the gate, can be purely paper-free and biomeric based. Similar to the existing T5 travel arrangements within the Common Travel Area.

The fascinating thing about this is that we are theoretically moving to a world without physical passports. If there is an e-passport on the Cloud, then the machinery will know who you are. And if you have an e-visa linked to an e-passport, then again the biometrics can link e-passport, e-visa, e-ticket and the biometrics to give Ready to Fly style sign off. My new Pakistan e-visa - a system they are trialling for 6 nationalities including UK citizens, is purely electronic and simply linked to my UK passport number.

For the OP, the data source was the information supplied at the time you applied for your passport. Biometrics aren't about glasses and hair colour, they are about the precise distance between your eyes, nose and mouth size (and hundreds of other measurements).