I've noticed that 2 days ago a lot of domestic and shorthaul flights had the cheap buckets removed, with the lowest available being K in Traveller, D in Club, even if the aircraft was virtually empty. When this happened before they did this for about a week until they had culled the requisite number of flights, got people rebooked, and then re-enabled for wider booking.
LHR only affected, LCY and LGW not showing this.