Hi Matty.
Before my selection I attended the CTC open day, and during one of the 'interview preparation' workshops, questions very similar to yours were posed. People were asking whether it matters if someone has perceivably 'long' hair, is an 'emo' etc. I know the latter is irrelevant, but their response was the same, "'well, what do you think?". They also echoed what others have alluded to regarding how interviewers perceive you, and how cutting your hair and turning up neat and tidy can only benefit you and how you will be perceived. Keep in mind that you'll be up against 11 or more other hopeful cadets, and anything you can do to set yourself apart from them and make a good impression is worth doing. The guys running the workshop were the assessors, and in fact turned out to be the very same people who put me through when it came to my day of assessment. Basically, the main theme of their responses was just "ask yourself". If you're questioning it, then you may have already answered your own question. If in doubt, crop it a bit! My hair was probably your length, and I cut mine before heading off to selection. I didn't go crazy, just tidied it up a bit. Made sense. Hope that helps matey.