When one retired from regular service, there was a huge stack of paperwork, including the dos and don'ts of uniform.
ISTR - and it's in the spirit (if not the letter) of 1358 - that the basic rules boiled down to 3.
1. Only ever No 1s or No 5s
2. Only when regular personnel would be wearing uniform.
3. If worn, standard of turnout must be up to regular standard (sic) - known as the no earrings or beards rule (unless you're a Prince!)
So - purely my interpretation - if regulars are wearing No 1s, then do so.
Questions arise: why at a Wedding and not a Funeral? And what are they going to do if you (apparently) transgress 1358?
And - as has been mentioned - this applies to Officers and (explicitly) not airmen.