For as long as I’ve been aware of pronunciation issues, I’ve understood that the /o/ phoneme in Received Pronunciation manifests as [əʊ] (in General American it’s [oʊ]). You can hear it in English media all the way up to the present day.
Here’s Hugh Grant (at 2:15, “No, no, no, of course not”)
But lately, I’ve been hearing English actors using what sounds much more forward and rounded, perhaps like [əœ]. I associate this kind of sound with Southern Hemisphere English (Australia, New Zealand, South Africa), not with England.
I’ve heard it in the mouths of several English actors, includingNatalie Dormer (at 3:30) and a few actors in Game of Thrones, including Isaac Hempstead-Wright (Bran Stark).
What you’re describing is a lowering as well as a fronting.
Pure fronting of [əʊ] leads to [əʏ]. The endpoint of the diphthong [ʏ] being approximately as high as the former value [ʊ]. What I hear Dormer saying in the audio example you linked to is actually [əʏ]. Fronted, yes, but still high at the end.
/o/ already got fronted in Valley Girl dialect back in the early 1980s. E.g., Moon Zappa’s famous enunciations. At 0:21 and 0:25 in this clip, we hear [øːʏ].
Being an American dialect, the diphthong is rounded all the way through, instead of the rounding beginning in the middle.
Not familiar enough with IPA to really follow the discussion. But I will observe that RP covers a range of different accents. The ones in your examples happen to be old-fashioned or at the “very posh” end of the RP spectrum, especially the Bertie Wooster one, which is an exaggerated pre-war accent.
Well my first thought upon hearing Natalie Dormer speak was that she must be a New Zealander who has managed to mostly replicate an English accent, but was belied by her /o/. I was surprised to discover that she’s English. No one else had that moment?
I can’t read the IPA, but I wonder if the shift you’re noticing is due to RP being influenced by Estuary English? The “o” sound in Estuary resembles the Antipodean variety.
Her “o” doesn’t sound Estuary to me. I’m going to attempt a bit of IPA here and say that Estuary “o” tends towards [aʊ] (but at that extreme the accent is more like full-on Cockney).