I am surprised by how "Australian" the people who left the UK in adulthood sound - perhaps to real Australians they still sound very British. I wonder whether it is because the rhythm of Australian accents are quite "catchy". I think there is a similar phoenomenon in New Zealand.

I am sure that you are right. I did not even notice my Dad's distinctive accent until I was in my late teens, by which time he had been away from his Raj-era boarding school for nearly forty years. I also knew a couple of octogenarians from Belfast whose speech, particularly when rapid, was still almost unintelligible to most NZers, even though I'm sure their familes back home would consider their accents greatly altered. It is apropos of nothing at all, really, but the sort of aural wilderness in which these migrated accents exist reminds me of my grnadparents' description of the late pre-teen years - too old for Mother Goose, too young for Lolita. I should probably add, that they said that twenty years ago! It just seemed to capture the "neither one thing nor t'other" quality of displaced accents.