I don’t think there’s a Britishism or Australianism at work here. Americans have always used “fully” as equivalent to “totally” or “completely”. It’s always been an option, and there’s nothing particularly British about it.
On looking back at Ben’s NOTE, I have to say that every example he gave of how Americans use fully, is how I would use it too and every example of what Americans wouldn’t say is what I also wouldn’t say.
I remember being puzzled about this when it came up before and scribbling various sentences on a scrap of paper to try to figure it out.
Agreed Sammy, I just left a comment on that post to say the same thing. I don’t know if you agree, but the examples given at the end of that post (e.g. “I’m fully going to ask her for a date”) sound like they could work when said in a Cornish or West Country accent. It’s based on nothing but a hunch, and I might just be guilty of horrible stereotyping, but that does seem possible to me. I’m actually visiting a friend in Cornwall this weekend, so if I remember I’ll ask her if it sounds normal to her.
Sorry but I don’t get the Cornish vibe, Rob. Not that I’ve been in Cornwall lately. It just feels odd and wrong to say I’m fully going to ask her and I don’t even know what it would mean. You wouldn’t say I’m comprehensively / completely going to ask her for a date. Or partially or minimally for that matter. You could say I fully intend to ask her for a date. Maybe it’s a garbled way of trying to say that. I’m fully going to ask Ben to stop attributing it to us Brits.
OK, so I asked her. A phrase like “I’m fully going to ask her for a date” sounded as weird to her as it would to you or I – so I think we can put that one down to confusion in this blog. But “fully amazing” and “fully brilliant” are things she’s heard people say, and she didn’t realise they were unusual until I asked her about it.
On Seth Meyers’ show 25/1/23 near the end of “A closer look”, he said “it may be crazy but it fully happened”.
Still not at all common here in England.
More on British/Australian “fully” here.
notoneoffbritishisms.com 
With reference to “sorted” earlier… the phrase “Full On” is also very “rave culture”. I’ve got two albums from the early 90s called “Full On”.
– Various – Full On (Deconstruction compilation 1993)
– Altern 8 – Full On .. Mask Hysteria (album, 1992)
Would you consider this Slate headline from yesterday an instance of this purported Britishism? http://www.slate.com/blogs/the_slatest/2017/08/17/steve_bannon_rules_out_a_military_option_in_north_korea_and_contradicts.html
I don’t think there’s a Britishism or Australianism at work here. Americans have always used “fully” as equivalent to “totally” or “completely”. It’s always been an option, and there’s nothing particularly British about it.
On looking back at Ben’s NOTE, I have to say that every example he gave of how Americans use fully, is how I would use it too and every example of what Americans wouldn’t say is what I also wouldn’t say.
I remember being puzzled about this when it came up before and scribbling various sentences on a scrap of paper to try to figure it out.
Agreed Sammy, I just left a comment on that post to say the same thing. I don’t know if you agree, but the examples given at the end of that post (e.g. “I’m fully going to ask her for a date”) sound like they could work when said in a Cornish or West Country accent. It’s based on nothing but a hunch, and I might just be guilty of horrible stereotyping, but that does seem possible to me. I’m actually visiting a friend in Cornwall this weekend, so if I remember I’ll ask her if it sounds normal to her.
Sorry but I don’t get the Cornish vibe, Rob. Not that I’ve been in Cornwall lately. It just feels odd and wrong to say I’m fully going to ask her and I don’t even know what it would mean. You wouldn’t say I’m comprehensively / completely going to ask her for a date. Or partially or minimally for that matter. You could say I fully intend to ask her for a date. Maybe it’s a garbled way of trying to say that. I’m fully going to ask Ben to stop attributing it to us Brits.
OK, so I asked her. A phrase like “I’m fully going to ask her for a date” sounded as weird to her as it would to you or I – so I think we can put that one down to confusion in this blog. But “fully amazing” and “fully brilliant” are things she’s heard people say, and she didn’t realise they were unusual until I asked her about it.
On Seth Meyers’ show 25/1/23 near the end of “A closer look”, he said “it may be crazy but it fully happened”.
Still not at all common here in England.