Its rapid spread could most clearly be perceived by comparing the accents of Diana, Princess of Wales, the Prince of Wales and the Queen, Professor John Wells, of University College London, said.
The princess would pronounce words like "Tuesday" and "reduce" more like "chewsday" and "rejuice". Other changes were also spreading from London and the South-east, the centre of the new pronunciation, where the "l" in "milk", "myself" and "middle" was being transformed into a "w", and the glottal stop was spreading like a rash into phrases such as "not only but also", which was becoming "no' only bu' also".
Professor Wells is carrying out a study of the advance of Estuary English, which is overtaking "Received Pronunciation" (RP) as the language of educated Londoners.
"Princess Diana is a very good example of generational change in pronunciation," he said yesterday. "Compare her pronunciation with that of Prince Charles, which is much more conservative; and the Queen's, which is much more conservative than his."
The differences in age - 12 years - between Prince Charles and his former wife indicated how rapidly "Estuary English" was establishing itself. "Diana still had an upper-class accent but it was different from Prince Charles's."
Another exponent of the new accent is Tony Blair, whose accent is noticeably more glottal when he appears on popular television programmes, such as the Des O'Connor Show, than when he is making a political speech. "Tony Blair exhibits flexibility, which is a good thing," Professor Wells said. "Your accent is a badge you wear, which tells people what sort of person you are. If you can be flexible, then you can fit in with many groups."
While the new pronunciation is spreading fast, the language's content is altering more slowly. It is partly, but not exclusively, driven by American modes of speaking: for example, Americans avoid glottal stops, and talk about "zeebras" where British children describe "zebbras".
Surprisingly, ethnic groups such as West Indians and Asians are having no noticeable effect on wider pronunciation.
Professor Wells is carrying out a study to see how quickly the new pronunciations are moving from the capital to other areas.
"The spread is not influenced by the media - newsreaders and soap stars don't matter; what matters is your peer group," he said. "The only way that the media matters is that it rapidly exposes more people to different accents than their own."
The new tide of change is the third to wash over English this century. In the years to the 1940s the distinction between "flaw" and "floor" disappeared, and the phrase "very sorry" lost its hard "r".
In the middle of the century, "sure" and "poor" began to sound identical to "shore" and "pour", and words such as "perpetual" acquired a "ch" sound in the third syllable.Reuse content