A Dahon struggles to meet the technical maximum size for a folded bike on the line into Kings Cross. This limit is really a fraction larger than a Brompton. My Dahon is slightly larger still, with handlebar attachments and a larger rack. However, it still folds properly. It's never been questioned. I've also seen Airnimals (bigger than Dahons when folded) and disassembled full-size bikes (both wheels out and stack the parts against the carriage wall), which have not been questioned either to the best of my knowledge. Personally I think calling a road bike with its wheels out a folder is pushing your luck. An Airnimal mostly takes extra vertical space, which is not really an issue, so I can see why that is accepted.