Just a quick update on this. I phoned and got my appointment with the NCS. I received my letter of confirmation of the appointment a couple days later. Stapled to the letter, on a little piece of yellow paper is a note which reads,
'IMPORTANT PLEASE NOTE If your photograph is not attached to your application form or signed on the back by one of your referees, then we will be unable to send your application in on the day of the appointment. You will be asked to take your photo away to get it signed then return it to us, thus delaying your application.'.
My thoughts are that lots of people were showing up to their NCS appointments without having stapled their photo to the application, hence the note that it must be attached *or* signed by referee. I guess someone could have their referees sign the form and then later attach a photo of someone else to the form. (Not sure what one would gain from that though).
Anyway, I will get it signed now *as well as* attach it to the form.