"I've never heard the word proven used by a Commonwealth citizen"

The word 'proven' is a common enough term in Scottish Standard English. There are other words which are thought to be more American but are also very common in Scotland like "gotten and pinkie" I think it is a mistake to think in terms like "British English" when in fact there are various types of British English.

It is like the full page article in the Daily Mail yesterday which claimed that Halloween was an American import virtually uncelebrated in Britain up until several decades ago. Of course it has always been a big to do in Scotland the only real difference now being that since the film ET kids tend to call themselves "trick or treaters" instead of "guisers".