For what it's worth, and I won't mention which panels I sit on, when I'm sitting on these I don't really tend to notice what people wear unless they wear something totally inappropriate or too casual for the occasion that it stands out - this could be more indicative that they knew what to wear as opposed to me being ignorant. If I'm wearing a full suit and tie (regardless of the weather), I would expect the person I'm interviewing to be at the same level. Exceptions made for the very young and inexperienced (i.e. no tie, or a proper jacket and trousers as opposed to full suit, etc). Every now and then I see people wear school uniforms but without starting a private vs public school debate, if you aren't wearing a blazer/tie (and maybe some nice pins/badges?!) then you are probably better off wearing a suit.
EDIT: It's probably worth mentioning I do not sit on this particular panel and never have.