can someone please help mrs clueless over here please ?

[thriftychic]

would it be a faux pas to turn up to a smart / casual wedding in a registry office wearing navy and white?
something like navy trousers , white blouse , burgundy jacket ?

I think that sounds fine. I only think white is a problem if you turn up looking like the bride!

Sounds fine, is the bride wearing a wedding dress? Is there a do after as you could guess a bt from that what to wear, maybe a shift dress with a boxy jacket you can take off if it's a smart lunch as well?

no, the brides not doing the whole white dress thing. We are having a meal afterwards and a knees up in a pub later . was meant to just be family but the numbers seem to be doubling by the day

Sounds like good fun!

Sounds great and you will look lovely I'm sure:)