On a similar note I was at STN today where a Swiss turned up. It was on the ground a good couple of hours so I guessed they were bringing the pax over, but no it seemed to me to depart empty. Surely it could have headed back immediately and not unnecessarily delayed later flights (if it was due to make any).
Perhaps the issue isn’t the capacity of SEN or the ease in which pax could theoretically be transferred, but one of waiting on ops decisions.
The Swiss couldn’t have made it back to LCY because it was too late. Perhaps BA were waiting to see if conditions improved. Perhaps the aircraft being displaced necessitated bringing in a new crew. Perhaps they couldn’t source a coach in good time. No point sending pax by train because it’s rail replacement.