Putting my old Customer relations officer hat on I read this thread with amusement.

The first thing I'd now like to do would be to read the CSD's report.
After all, they crew might have had better luck in identifying what actually WAS in the salad.... as the OP seems confused as to whether it was "fly/insect/mosquito".... or possibly a bug menage a trois?

If it was indeed a flying insect then quite possibly how this could be ANYONE'S fault, other than the little critter itself is beyond me!?

It did used to amuse me no end when people complained about situations arising in certain outports as if they expected them to be akin to Royal Tunbridge Wells on a Bank Holiday afternoon. We always got many 'I spent 5 days in Calcutta and the minute I ate the in-flight pretzels 15 minutes after take off they gave me listeria, salmonella and pig flu!' complaints.

Of course it is certainly possible that there is a fly infestation in the Airline Catering kitchen in BOM that BA contracts for its First class meals, in which case the reporting of this to the South Asian Catering manager is wholly sensible. They will be able to add this to his/her usual check list (although I'm sure it already is) for their very regular visits to the facility.

Yet I actually quite like the OP's letter.... they manage to be succinct. They list the facts (albeit I would have preferred a positive identification of the bug), and offer enough praise for the crew to make me to feel they are being somewhat reasonable.

You First offer the absolute standard holding line for a complaint from a First class passenger (most airlines these days tell CRD staff to always apologise immediately) but I'd expect a more reasoned reply from Customer Relations.... something along the lines of .....

"hey we're sorry, but we really are not liable for a fly/mosquito etc flying around Mumbai."

Of course this could always simply be a troll.... but its been fun anyway.