Flapping

This is an interesting phenomenon of Engish phonetics, and it seems to be spreading. I have a few questions:
1) Does anyone know when it is thought to have begun? I've noticed that older speakers, like my grandmother, flap /t/ and /d/ much less frequently than I do--it's manditory for me before unstressed syllables, very frequent across word-boundaries, and optional following /n/.
2) It occurs in Australian English as well as North American, but it seems to have become common later, and is regarded by some as an American borrowing. Is this true? Also, Wikipedia says that Australians sometimes flap the /t/ in 'thirteen'. Is that true? Does flapping occur in New Zealand or South Africa?
3) Flapping seems to be on the rise in English English, Estuary in particular. From what I can tell, it's limited to word-boundaries, but I've never seen a description that stated that. Does it occur word-internally in England? More specifically, for Scouse, are there any homophones that result from both /r/ and /t/ being realized as [4] in some situations?
4) In Hiberno-English, what is the distribution of the flap and the slit fricative for /t/?

I have heard some Australians flap the /t/ in "thirteen" and "fourteen". And I agree with your observation that flapping seems to be increasing in English English". JC Wells actually mentions this on his blog: http://www.phon.ucl.ac.uk/home/wells/blog.htm . He says that flapping is very common in function words, in cases like "as it is", "that it's", "but if", "at a", "what about", "a lot of", "a bit of", "not exactly", "get elected".

Sorry for the rogue quotation mark in my previous post.

I think I've heard it occasionally in some British dialects like the northern English ones, but don't quote me on which ones exactly.

To me it seems like a latent tendency in most varieties of English that happens to have been taken to extremes in some dialects (like North American, where it is pretty much mandatory) while being found more modestly or not at all in others.

>>1) Does anyone know when it is thought to have begun? I've noticed that older speakers, like my grandmother, flap /t/ and /d/ much less frequently than I do--it's manditory for me before unstressed syllables, very frequent across word-boundaries, and optional following /n/. <<

On the other hand, my dialect has been reducing flaps to nothing altogether, especially in very unstressed speech (such as many cases of "getting" and "kinda") and before syllabics other than [n=]. My own idiolect though is more progressive than many in this regard, though, even though it is still very common here on a more limited basis.

Besides flap elision, though, my distribution of flapping is similar to yours except that I also flap consistently after /r/, when I don't elide the resulting flap.

<<Besides flap elision, though, my distribution of flapping is similar to yours except that I also flap consistently after /r/, when I don't elide the resulting flap.>>

I forgot to mention that. I flap after /r/ as well. I've noticed recently that I sometimes elide the flap as well, or replace it with a glottal stop. It seems to be most common before '-ing' and '-y' endings. I haven't figured out all the rules yet.

>>I forgot to mention that. I flap after /r/ as well. I've noticed recently that I sometimes elide the flap as well, or replace it with a glottal stop. It seems to be most common before '-ing' and '-y' endings. I haven't figured out all the rules yet. <<

Before "-ing" seems to me also like one of the more common places where flap elision occurs here, aside from before syllabics other than [n=].

Yeah, I often do flap the /t/ in "thirteen" & "fourteen".