Queen Elizabeth II's famous cut-glass accent, the Queen's English, is now sounding less upper-class, a scientific analysis of her famous Christmas broadcasts found.

Researchers analysed each of her messages to the Commonwealth since her 1952 accession using digital technology to track the shift in her pronunciation from the aristocratic Upper Received to the less plummy Standard Received.

Jonathan Harrington, professor of phonetics at Germany's University of Munich, wanted to discover whether dialect changes recorded over the past half-century would take place within one person.

"As far as I know, there just is nobody else for whom there is this sort of broadcast archive," he said.

He said the aristocratic way of pronouncing vowels had gradually ceased to be a class apart over the decades.

"Her accent sounds slightly less aristocratic than it did 50 years ago. But these are very, very subtle and slow changes that we don't notice from year to year," he explained.

"We may be able to relate it to changes in the class structure."

He told The Daily Telegraph newspaper: "In 1952 she would have been heard referring to 'thet men in the bleck het'. Now it would be 'that man in the black hat'.

"Similarly, she would have spoken of 'the citay' and 'dutay', rather than 'citee' and 'dutee'. In the 1950s she would have been 'lorst', but by the 1970s lost."

The queen's annual broadcast is a personal message to the Commonwealth.

A Christmas institution, the 10-minute broadcast is televised at 3:00 pm in Britain as many families are recovering from their traditional turkey lunch.

The results were published in the Journal of Phonetics quarterly magazine.