Both 255 and 237 aircraft were already parked at gate before the delays started piling in. So though they were mildly affected, it wasn't as serious as 251.

255 boarded on time and left a hour late because push back vehicle wasn't available.

Forgot to add: When we finally arrived at LHR at around 10:15am, we were all told to stay in our seats, police came in and headed straight to economy (not sure about the reason? possibly delay frustration related?). That took another few minutes and said DM just stormed out the plane.

Both 251 and 237 delayed till 1:20 initially, but 237 proceeded to board at 1:20 while 251 was further delayed.

I think what he wanted was to swap the aircraft so the 3 flights still departed in the same sequence, so 251 takes first available aircraft, 255 second and 237 last. He requested this when 255 was all boarded and ready to leave, so that realistically leaves the 237 aircraft which is only 3 class configured..