A paper presented at the British Association Festival of Science at Cardiff University traces the evolution of received pronunciation from the early 20th century to the present.

In it, Professor John Wells of University College London describes how a well spoken Englishman once pronounced a word like "cloth" as "clorth" and used a clipped r-sound between vowels in a phrase such as "very sorry".

But in the mid-20th century, words like sure, poor and tour started to sound identical to shore, pour and tore. People started to insert a t-sound in words such as prince, making it sound like "prints", and a "ch" sound became respectable in words such as "perpetual".

Now, in the late 20th century, "ch" and "j" sounds are spreading into words such as Tuesday (often pronounced "choosday") and reduce ("rejuice").

Resistance

Prof Wells said: "The newer pronunciations may be heard in the speech of young people whose parents would blanche to hear them."

He said it was no longer true, if it ever was, that all educated people spoke with received pronunciation.

"Even received pronunciation itself is gradually changing, largely due to influence from the speech of London and the south-east - the accents sometimes known as Estuary English, which nevertheless may encounter resistance in other parts of Britain, as well as from those who dislike change of any kind in language."

Prof Wells said it was too soon to say whether demographic changes, notably the influx of West Indians and south Asians into the UK, would have any lasting effects on pronunciation.

But he pointed out that the pronunciation of ask as "ax" was no longer restricted to "quaint rural dialects".

"On the contrary, it has become an urban black characteristic."

Accents

Prof Wells draws a distinction between "the Queen's English" or "Standard English" - standard in respect of grammar, vocabulary and usage - and the way English is spoken.

"Standard English can be spoken in a variety of different accents," he says.

"All educated Scots can speak Standard English. But very few of them use received pronunciation.