Thanks for that encouraging note Thomas - if only it were possible to do that with British Airways!
I did call their 'Customer Service' desk last week, specifically to ask for advice about how to package the bikes, given that we'll be flying to and returning from different airports. And our tour is over the Himalayas, so we won't be able to carry large, heavy bags/boxes. I described my plan to do exactly as you said - use plenty of bubble-wrap and a large, clear plastic bag, all of which could be discarded at the destination, but I was told flatly that this would NOT be accepted and "bicycles must be packaged in a recognised bicycle bag or box". So I offered to use bubble-wrap and a large cardboard box, the sort that new bicycles are shipped to the retailers in. All I got was a frosty "NO. Bicycles must be packaged in a recognised bicycle bag or box". So I asked for a definition of 'recognised bicycle bag or box', and she simply drew my attention to the three tiny cartoon diagrams on their website, which was in front of me at the time. I offered to use a coloured plastic bag instead of a clear one, and attach duct-tape handles to it so that it looked like one of the diagrams, but I got exactly the same response. So I asked to speak to the manager, who was confrontational from the outset and refused to offer any advice or suggestion, apart from what is written on the website. It all turned really nasty and I ended up shouting at her - "It's people like you who make living in the UK so CRAP!", which was probably a mistake since she knows my booking reference number. Anyway. We're going to have to buy cheapest possible bicycle bags and throw them in the bin at one airport in India, and then see what compromise we can arrange at the other on our way home (at least the trip will have finished by then).
Ironically, and to add insult to injury, one of the diagrams they cite as a 'recognised bicycle bag or box' is in fact an accurate representation of a 'real' box, but the real box exceeds BA's maximum permitted dimensions!
Wish I'd seen this before I booked with British Flippin' Airways