Is a green waistcoat and grandad shirt acceptable attire for a formal wedding (as a guest)?

Posted by twitchy-the-clown@reddit | AskUK | View on Reddit | 38 comments

Its days away in May and I'm cash strapped, its a family wedding, fairly low key affair and all I have to wear is a formal green plaid waistcoat (the one with the shiny fabric on the back), a collarless shirt and blue linen trousers. People I've spoken to have told me I should wear a tuxedo or at the very least a suit. Thanks in advance I'm totally clueless.