Data point from today (Monday 5th Feb).
Booked on the BA1399 (1450 MAN-LHR). Travelling with luggage so didn't do online checkin. BA says checkin opens 2h30 before flight (so 1220). Airport staff flitting around the desks loading up computers, messing with tags and labels. Chatting.
Started processing passengers about 1243, but called passengers from the general check in line before the Priority queue, until the girl who was doing the Priority check in was ready.
Security though was a breeze, absolutely no queues at all. In and out.