I'd completely forgotten that I'd decided that because we have wired machines on the network too, it wasn't worth writing down (and losing) the 24 bit wireless password on the manual, because it's a pw that is easier to reset than to transcribe, and the control panel is self-explanatory anyway: all I needed to do was use a wired machine to access the cp.
Finally found a backup router conf file on my hard disk and remembered this decision (which seemed so self-evident at the time). Bah! I wish my brain worked better. I only set this up in July. My brain makes me angry. I'm sure it used to work better than this.
Now, what was my name again...?