Famously in "huntin', shootin', and fishin'." But I'm not sure it's the upper classes emulating the lower. It seems to be parallel evolution from different forms of Old English [0]. Which makes sense; it's unlikely an upper-class English person of the 1920s would be motivated to copy lower-class speech patterns. Bertie Wooster wouldn't want to sound like his scullery maid.

[0]: https://books.google.co.uk/books?id=YMS3AwAAQBAJ&pg=PT26&lpg...