The original plan years ago was to replace them with LHR aircraft. Then the Monarch slots came up, which left BA short of aircraft and crew. The training of crew is proceeding, some slots were leased out pending arrival of new aircraft.

Just as the new aircraft are being delivered, that would release those old aircraft, Thomas Cook have gone down. Some of the leased Monarch slots went to Thomas Cook. Those have now returned to BA. Under the use it or lose it rules,BA must find more aircraft and crew to use the returned slots. BA are talking about acquiring some of the other Thomas Cook slots, but in reality they have neither the crew or aircraft to operate them.

Eventually those aircraft will go, and be replaced by LHR A319's, when they can be released.

The B737max LOI is looking shaky. The return to service is looking likely to be postponed again till spring at the earliest, causing Boeing to cut production again. Unless some airlines take the opportunity to cancel orders, BA have no chance of receiving there aircraft in the time scale specified in the LOI.