I bet they are 1970s Deco revival. Biba apparently used to sell a line of Deco style jewellery like this but it wasn't stamped Biba, and is often resold as real 1920s-30s jewellery. I know this only because a woman who donated a lot of things to our Fashion History Museum sold most of the jewellery she had bought at Biba as 1970s Deco style jewellery at a house sale, but later found much of it listed on eBay as authentic 1920s/30s Deco jewellery. Anyway, I am not sure if these are Biba, but the trend for making Deco jewellery in the 1970s was certainly taken up by them!