Not something you'd ever need, I guess, Keith!
They were pieces of jewellery, often made as a matching pair, which could be attached by means of the clip at the back onto a plain dress or jacket to dolly it up.
Having talked to some of the folks on the Vintage Jewellery group on Facebook, it's been suggested by Janice that this might be a hat ornament rather than a dress clip. Now I didn't know about hat ornaments either!