are they called 1 direction or one direction? x factor

are they called 1 direction or one direction? x factor, what is the correct way to say 1 direction or should i say one direction, or does it really matter, i notice that there name just seems to change from person to person.

though saying that on the x factor shows i think they say one direction, so that might be the correct official way to say one direction, to write it and not put it there band name as a no.1, though of course they will be looking to get a no.1, just not be called 1 direction though.

it is easier to put the bands name as a 1 though then actually typing out one, so maybe people calling them 1 direction are just being lazy?.