We flew from Bordeaux with easyjet on sunday after the recce. Two us used £1.50 dustsheets that were far too thin and fragile, light to carry but not up to the job really. Two used the CTC bags, which were brilliant but a tenner more and heavier to ride with.
In the past I have used mattress bags, they are also good, and free.
Leave the wheels in. Twist handlebars and turn them so they are down, if you see what i mean, but also twist your sti units so they are inside the handlebars and protected by them. Put a pedal strap or rope around the front wheel and tie it to the frame so it doesn't flap about, this makes it much easier to put the bike on a trolley, upright so it is not too wide to fit into doors.
Drop the saddle as far as possible. Remove pedals but then put them back on inside, so one of them protects your big chainring if the bike is dropped eg on to a kerb. Remember the check-in staff are worried only that you have paid for the bike space, while security have a different agenda: so put the valve caps at 6 oclock and remove valve caps and cut a small hole near them. If you are then told to let the air out, do so easily and quickly. In Vienna a security guard put his Stanley knife through the front tyres of our bikes to let the air out. Get there massively early, allow an hour to fettle the bikes and plan to be the first at check in. We allowed three hours from arrival at the terminal to take off and made it by 10 minutes, too close for comfort. Remember you may have to check in at one place and then go half a mile to oversize luggage where they will want to lay it on a conveyor belt and wave goodbye to it, then return to the first check-in, and in bordeaux that is a different building and on a different floor so we had to get four bikes and four trolleys from one terminal to another and back again. In crushing heat and lots of fat people getting in the way, you will wish you had just ridden home.
Hence dropping the saddle to get it into the scanner, if you have straight bars you might want to loosen the holding nuts on the stem and shift the bars backwards so the end of the bars at the front of the bike is lower.
I prefer to remove rear mech and tape it so it is inside the chainstay, others do not.
BA are good to fly with but i would not risk the pannier idea, if you do not have a bag to put it in just either check it into the hold with your puncture repair kit and its glue, plus all your metal parts, or put it in a big plastic bag, as gordon did, and tape the whole thing up with parcel tape. Remember you will need a small knife for cutting tape so when you have fettled the bike, do remember to slip that knife into your hold bag. Two armed policemen were called to deal with me when i forgot the penknife in my pocket at gatwick. Not something i will forget again.....