I get the impression that in the "classical Received Pronunciation" of English during phonetician Jones's era, the lenis plosives /b/, /d/, /g/ (and probably the affricate /dʒ/ as well) in initial position were more voiced than the English of today's Britain. Additionally, were the fortis plosives /p/, /t/, /k/ (and /tʃ/) any less aspirated? By "more/less", I mean both in voice onset time and in the frequency of the feature's occurrence. Can anyone confirm or refute these claims?
English (at least in the present-day) can be characterised in terms of VOT as having short-lag (voicing beginning soon after release) versus long-lag (voicing begin some time after release) plosives whereas some languages, such as Spanish, have lead (voicing beginning some time before release) and short-lag plosives.
So you appear to be suggesting that plosives in the upper-class British English of a century ago were more like modern Spanish plosives. It would be helpful to understand where you get this impression. As @jlovegren says, a half-decent recording of Jones or someone else from that era could easily be used to test the hypothesis (so you could confirm or refute the claim). For what it's worth, my impression from listening to Jones is that the hypothesis is not correct.