Its a lovely dress, I think if i saw someone wearing it I'd reckon they were giving a nod to the vintagey style which is not a bad thing at all! 
i agree with whoever said that people tend to dress down a bit for formal lunches in London, i could imagine some student friends wearing that for a formal lunch out in York/BAth!
accessories would depend on your colouring/height/build OP? maybe just nude ballet flats (or heels like the model has on) i think over accessories would make it a bit too fussy/costumey.