Get on the Mess Comittee and have a Rabbie Burns Night at the beginning of the year, failing that get a singleton multinational/exchange post then you can wear whatever you want just don't get caught out........
I believe that, somewhat surprisingly, the etiquette for wearing a tartan (kilt or trews) is that you need to be British, not necessarily Scottish or claiming descendancy from a clan.
Personally, I don't think that many Englishmen would be terribly comfortable with that idea, however as Cornishmen my brother, father and I all wore cornish kilts for my brother's wedding and damned dapper we looked as well!
Clearly, if the above mentioned fella was at 5, then standards have slipped drastically! Still, only to be expected with bl00dy locators running all over the place.
The wearing of a kilt/trews with naval mess kit is common in the wardroom the-matelot, and it commonly described as 'slater's rig' after Sir Jock who thought it would be a damn fine idea.
More significantly, all this boll0cks about the wearing of tartans associated with clans stems from Sir Walter Scott and the romantic vision of Scotland he created. If you want to wear a kilt, pick one and stick it on. The chicks dig it.