Tui will be restarting some flight again end of this month , ACE TFS and from December, INN.
Flew out of LTN a few days ago, it was a pleasant experience. Security was a breeze (less than 3 mins all in, unlike the airport at the other end), masks on for everyone, plane was probably 30-40% full so plenty of space to move around in case someone sat next to you (with permission of course).
On the way back passport control was quick too. Out of airport in record time.