IIRC, in the good ol' days of slam-door stock on the Southern Region (class 421?), you could load the bike straight into the integral guard's van (Mr Nice Friendly Guard as often as not offering a helping hand), step in through the same door yourself, then walk along the corridor to the nearest passenger section. No holding up the train. No problems. No frantic scurrying up and down the platform looking for the proper 'bike' section (as happens nowadays). Indeed it was easy to tell, as the train was coming in, exactly where the guard's van would be, seeing as the guard was clearly visible leaning out of his open doorway...
Ahhhh! The good ol' days!