English as spoken in England has some regional dialects and many regional accents. There is also a prevailing accent which is to some extent a regional accent of the South-East, around London and the two universities of Oxford and Cambridge, but which is also a standard or educated accent.

It was formerly associated more strongly with class, but in the longer historical picture, it is really just an accent flowing from London and the majority centres of population, gradually influencing other forms of English over hundreds of years. The London influence was strong already by Chaucer's time.

I am using the vague term "Southern British" to cover this. But there are some regions in the south that it is not applicable to. The West Country (Cornwall to Dorset) has its own distinctive accent, which however is much influenced by the eastern accent. Furthermore, Inner London has its own very different dialect, traditionally called Cockney. This is radically different from what I might call "Standard London", though sound changes often originate in Inner London and propagate out into the more educated varieties.

For example, the vowel A followed by S, F, or TH has become [a:] AH (as in 'father'): as in 'ask, pass, half, after, path, rather'; especially in the commoner words. This pronunciation also occurs in South Africa and Australasia, so it probably pre-dates their colonization. But until very late in the nineteenth century it was stigmatized as a vulgar, "Cockney" pronunciation.

(I've revised this node to use IPA transcriptions in addition to ad-hoc respellings.)

The loss of R before a consonant or at the end of a word was complete by 1800, but educated speakers around then still tried to pronounce it: Keats was castigated as "Cockney" for treating words like 'laud' and 'lord' as the same, [lɔ:d]. But it was clearly the normal London (and Australasian) pronunciation by then.

In the twentieth century three major sound shifts have been identified. Well, the separate changes described here are not part of a single change, but separate innovations that generally happened at the same time.

First sound shift

The earliest representatives may be heard in old films, where the upper-class characters are being "teddibly" decent; and HM the Queen's strikingly old-fashioned pronunciation still contains some of these features, though she has actually changed over the years.

This earliest 20th-century Southern English had long [ɔ:] "aw" vowels before S, F, and TH, as in 'cross, soft, cloth'; this changed to the short [ɒ] "o" sound these words now have for most speakers. Note that the change from "aw" to "o" was a middle-class change, so the old "aw" vowels are still heard in both upper-class and lower-class speech.

Another change was the loss of the [oə] "oah" vowel in 'floor'. This became the same as the [ɔ:] "aw" vowel in 'flaw', so that 'floor' and 'flaw' are now homophones. No common accent that I'm aware of retains the "oah" sound.

A third change was of intervocalic R. It used to be a flap [ɾ], as in Spanish or Japanese, which sounds to us like a very short D: so we might represent 'very' and 'terribly' as "vedy" and "teddibly". In the early twentieth century this changed to the same R [ɹ] as used at the beginning of a word.

Second sound shift

The result of those changes was the Received Pronunciation (RP) of the early to mid twentieth century, spread by the BBC, recorded by phonetician Daniel Jones, still spoken by many older educated people, and until recently thought of as a prestige accent. Now it's no longer such a prized thing to sound posh. It might seem unchanging, because it can still be heard, but even standard accents continue to change.

Then came the second sound shift.

The diphthong [ʊə] "ooa" was lost, becoming [ɔ:] "aw": so 'poor' and 'sure' changed from "pooa, shooa" to "paw, shaw".

The [tju:] "tyoo" and [dju:] "dyoo" sounds of TU and DU in unstressed syllables became [ʧu:] "choo" and [ʤu:] "joo". So 'fortune, graduate" changed from "FAWtyoon, GRADyooayt" to "FAWchoon, GRAJooayt".

The letter T changed to a glottal stop [ʔ] before another consonant: so 'quite nice, not really' became "qui?nice, no?really".

A final I-vowel, which was formerly a short [ɪ] "i", became a short [i] "ee". So where 'city' used to have two vowels the same, just like 'civic', now it is more like "sit-ee".

The vowel of 'cut, come' in older RP is a peculiar sound that has no real equivalent in any other language: the phonetic symbol is an upside-down v [ʌ]. This changed to a short form of [a] "ah" as in 'father', so that now 'cut' and 'cart' differ only in the length of their vowel, as do 'come' and 'calm'.

This is approximately my own speech, and I feel quite conservative in speaking like this now.

Third sound shift

In recent years there was been a new shift, and this new form is called Estuary English because it is not specifically London but goes all the way down the Thames Estuary. It has also been reported to be influencing local accents in Milton Keynes and Liverpool. It is still more common among younger people, but within the next generation it will certainly be the standard educated speech of England. Its features can be heard in all classes including royalty.

The glottal stop now also occurs between vowels and finally: so 'not a lot' is [nɒʔ ə lɒʔ] "no?alo?".

The change of "tyoo, dyoo" to "choo, joo" now also occurs in stressed syllables: so 'tune, dune' are "choon, joon". But this is widespread: even BBC Radio 3 announcers now say it.

The letter L before or after another consonant, or finally, has become W: so 'milk, middle' are now "miwk, mid-w". (Actually the exact representation of this sound is debatable: some phoneticians write [mɪok].)

And those occurrences of the letter R that are still pronounced are often (not among all Estuary speakers) changed into a kind of W, or a rounded RW: phoneticians I have discussed this with are unclear about the exact nature of the change; there has been no through study of it that I know of. My own impression after much thought is that it's the older R with advanced tongue root added; or maybe I just can't make the sound properly.

Stress and length

In addition to more systematic changes, a lot of individual words have fluctuated. Many of these are matters of stress: "forMIDable" and "hosPITable" are gaining out over "FORmidable" and "HOSpitable", while "CONtroversy" vs "conTROVersy" is still wide open. Others are matters of short or long vowels: "stabilize" once had the short sound of "stab", but has assimilated to the related word "stable". Do you say amenity as "aMEEnity" or "aMENNity"? Often two pronunciations compete because they are each supported by rival analogies: should subsidence be "subSIDEnce" like "subSIDE", or "SUBsidence" like "RESidence"?

Part of this fluctuation is due to American pronunciations having an influence, but the nature of English stress and vowel length means that these analogies and competing principles of regularization will always be around.

The future

It would be rash to predict too much, but here are some observations on the speech of youngsters in inner London, which I suspect will increasingly affect the standard accent over the next generations. Some of these changes are characteristic of Black speech but are now heard in children of all races.

Diphthongs are becoming monophthongs: the [laɪk] of like has become [la:k] and the [seɪ] of say has become [se:]. But this new laak sound is not the same as standard lark, because that vowel is moving back to [ɑ:], almost [ɔ:], as if lawk.

There seems to be a chain of changes going on. The original aw vowel has broken up into [oə] or [oɐ] (oh-a or oh-ah) in modern Cockney. The second part may have a distinct ah sound to it, and this is also happening to the neutral vowel when final: so water is shifting from [wɔ:ʔə] to something like [woəᧉɑ] woa'ah.

Rhythmic accent is also changing to a more staccato or glottalized delivery. I'm not sure how to describe it better.

I got some of these facts from studies by Professor John Wells of UCL. See for example
www.phon.ucl.ac.uk/home/wells/changingscene.pdf
A much more detailed study of modern (Estuary English) forms is available at
www.phon.ucl.ac.uk/toc/set_people.htm
but you almost certainly need to be British and understand SAMPA to be able to read it.