Arrived from an Amber list country travelling on BA 2 days ago - arrival into LHR T5. I was wearing my airline uniform and ID.
Within seconds I was approached by an airport employee, asked if I was exempt (yes) and escorted into a line for ‘exempt’ travellers.
I was seen by a border control employee within seconds who asked for my passport and nothing else, and within 5 seconds of the passport check I was through, no further questions asked.
I must admit I was astonished, but it seems if you are able to fall under an exempt category, the chances are you will be processed very quickly (at least at T5..).