I flew from Denver to Sicily and back with a stopover in Dublin on British Airways last May, all I did was roll my bike up to the check-in counter, turn the handlebars sideways and take the pedals off. They gave me a plastic bag for the Denver-London leg, otherwise the bike went unboxed and unwrapped. I did the same thing 4 years ago when I toured Scotland. They might have different rules for different routes, though.
They seem to waive the size restrictions for sports equipment, nobody said anything about the size of the bike (and it very obviously was bigger than the limits).