If it's a Mess function, then the answer, surely, must be Uniform Nos 1s with bow tie or Mess Dress only (neg min medals unless so directed) - unless you are a civvie guest when lounge suit/evening dress would be worn?
This is the rig we had to wear when I was in the Mess in the 70s. But in those days there wasn't a miniature PO rate badge available, so I took a liberty and wore the tie pin (originally a shirt collar badge which noone seemed to like and few ever wore) on the lapel - encountered no problem from the Pres.
But then, uniforms seemed to have changed slightly ..!?
Is there a Royal Naval kilt :scratch: - and could it be mainly blue with thin red and thin white stripes .. and can I claim the patent if there isn't !!