Similar case for me on Monday 31/7. Day before after checked in online, the 1498 was changed from A320 to A321. Surprisingly my seat was reallocated from exit window to exit window.

Anyway, arrived at LHR from DME and checked my booking to see a new departure for the 1498 estimated at 21:37hrs (20:55hrs std). Check on FR24 and the flight was due to be operated by G-EUXD. Quick check where EUXD was coming from and it was operating the SPU-LHR which had diverted on the inbound to SPU.

When the aircraft eventually arrived, there were a couple of announcements at the gate before boarding apologising for the delay with the explanation that the original scheduled aircraft had been swapped to EUXD but that had now been delayed. Don't know if that had been another 321 that was due to operate the flight or if talking about the original 320.

Eventually had wheels up at approx 22:00hrs and deplaned in GLA just after 23:00hrs. Don't normally get the late GLA flights. Are they prone to creeping delays?

S