Originally Posted by
psychopompos
I might be completely misunderstanding the situation, but isn't the delay of the outbound flight covered by UK261? BA119 had to divert due to extraordinary weather conditions and therefore the airline doesn't have to pay out compensation, however the extraordinary weather conditions didn't apply to BA 118 on which the op traveled.
If it's extraordinary circumstances on the outbound, to a location which isn't an airline hub, then it usually carries over to the inbound, since BA can't reasonably rustle up a spare 777 at Bangalore. However there is always a "all reasonable measures" clause, so for example if the BLR turnaround time was 12 hours then BA would be expected to cut that down to 9 hours or whatever. But in this scenario, unless the OP can give a decent "all reasonable measures" line then I can't see it applying.