Art Deco brooch

Hello, This is a ca. 1935 Art Deco bar brooch (white period?). It has 15 Old European cut diamonds and 10 rose cut accent diamonds. The centre diamond is approximately 65 points. Total diamond weight is about 2.50ct. The setting is platinum over 18kt white gold, with a navette setting for the centre three diamonds and cut corners on the ends. It was purchased in New Zealand where I live, although it is believed to have been made in England. ANY HELP you can give me identifying the monogram from the box would be great! I have seen the same one at a jeweller's shop in the Queen Victoria Building in Sydney. They could not identify it. Bye and thanks, Bill