I don't get why there are so many comments saying it isn't suitable.
I think its perhaps because I do not live in the UK, and things like this just don't really matter that much here.
My aunt, who is quite flamboyant (but from the UK) wore a pure white jumpsuit to my wedding. I didn't bat an eyelid or even think anything of it.
To be honest there would be more of a raised eyebrow if someone wore black to a wedding, rather than white.
I think the dress is beautiful and would be perfect for a wedding. Its hardly going to upstage the bride, seeing this is a floral flowy dress and not a bridal gown.