With all respect I think the date is later. The Paris-invented cloche hat worn by both women in the foreground was popular throughout the 1920s and a little bit into 1931/1932. There's another woman wearing one in the background, suggesting that the style was well-established by then, so the photo could date to the mid- to late 20s. (It's Portsmouth, not Paris, after all!)
With all respect I think the date is later. The Paris-invented cloche hat worn by both women in the foreground was popular throughout the 1920s and a little bit into 1931/1932. There's another woman wearing one in the background, suggesting that the style was well-established by then, so the photo could date to the mid- to late 20s. (It's Portsmouth, not Paris, after all!)
