flatlander

It's my further understanding that BA standardising on an Airbus short haul fleet was partly to be able to use containers (ULDs) for all baggage, to have a standard (and less labour-intensive) way to load all aircraft.

The 737 (and derivatives) hull design is old enough that it has inward-opening doors, as it was designed before there was high confidence in outward-opening door locking mechanisms. Therefore it can't handle containers well, as you can't put the last container in just behind the door and close the door as you can with an outward-opening door. Also, the hold is not ULD-shaped.

The A320 (and derivatives), being newer, was designed with outward-opening doors and ULD compatibility from the start.

LHR T5 does have a few baggage belt loaders but you rarely see them in operation - if you look at the stand equipment around LHR T5 aircraft the belt loader is conspicuous by its absence, compared to somewhere like Stansted where almost all baggage is loose-loaded (Easyjet, Ryanair, etc). Instead, a set of ULD trolleys and a container loader is present.

cgtechuk

I enjoyed my last JetTime flight was a bit different and meant no BoB