How the Queen's cut-glass accent is slipping: Videos reveal the monarch has shifted her speech in recent years to sound more like one of us

Her cut-glass accent is considered the very definition of Received Pronunciation in the English language.

But it seems even the Queen herself is no longer sticking to the so-called Queen's English when talking in public.

Researchers have found her accent has subtly shifted to become more 'middle class' over the decades as her vowels have shortened.

Scroll down for videos to see how the Queen's accent has changed 

Analysis of Queen Elizabeth II's Christmas messages have found that her pronunciation has changed between 1957 (left) to 2015 (right) to become more middle class as her vowels have shortened. For example the way she pronounced family changed from 'femileh' to sounding more like 'fameli' in recent years

Scientists studied Queen Elizabeth II's Christmas broadcasts throughout the years to examine how her pronunciation has changed.

They said there has been a slow shift during her 64-year reign that has seen the Queen's words become more clipped and less aristocratic.

While she still maintains the correct grammar and vocabulary from earlier in her reign, the Queen, who turns 90 this year, appears to have subtly changed her pronunciation of certain words. 

For example, the way she says family was phonetically more like 'femileh' in 1957, but in 2015 it had changed to sound more like 'famelee'. 

Similarly the way she pronounced the word lost has changed from 'lawst' to something similar to 'lowst'. 

Professor Jonathan Harrington, a phonetics expert at the Ludwig Maximilians University in Munich, and who led the research on the Queen's accent, said the change likely occurred subconsciously. 

He said it is likely the monarch's accent has shifted as the people around her have changed through the years.

Her grandsons, Prince William and Harry, for example, have accents far closer to Estuary English than their father, for example.

Estuary English was originally considered to be the regional speech used by people living in London and the south East of England.

In recent years it has been adopted by many upper and middle class people to give them a faint Cockney accent, while still using standard grammar. 

It is likely the accents of her staff have also changed while the accents she will be exposed to when watching television have shifted considerably over the decades.

Speaking to MailOnline, Professor Harrington said: 'What has happened in the last 50-60 years is that upper-class-RP has shifted towards mainstream RP and mainstream RP has shifted towards London Cockney giving rise to Estuary English. 

'The Queen and others have been swept up in this change so that the Queen's accent is now more mainstream RP and less aristocratic than it was in the 1950s. It is now positioned closer to mainstream RP than it was in the 1950s.'

Professor Harrington said cultural influences can have a major impact on a person's accent.

For example, when the Queen made her first televised Christmas broadcast in 1957, at the age of 31, her fellow broadcasters on the BBC used similar accents.

More recently, however, regional accents have become more popular on television channels and programmes from the US are incredibly popular on terrestrial British channels.

Writing in the Journal of the Acoustical Society of America, Professor Harrington said the gradual lexical changes in the Queen's speech appeared to be caused by 'levelling due to variation in dialect contact, increasingly with middle class speakers for the Queen'.

Speaking to BBC Future, the professor said it was common for people to alter their accents very slightly to match those they are talking to. 

The Queen's accent may have been subtly influenced by those around her including her grandson's Prince William and Prince Harry (pictured) whose talk with an accent more approaching Estuary English

Scientific studies in the last 10 years have shown that when we talk to each other, we often subtly imitate each other's speech and indeed also gestures even though we don't realise we are doing this,' he explained to MailOnline.

'The changes in one conversation are of course very subtle and not noticeable but accumulate over time. 

'So as the aristocracy increasingly came into contact with the middle, and lower, classes in the 1960s and 1970s, accent change was inevitable, just as a consequence of this type of subtle and entirely natural imitation.'

'We can only speculate of course, but as far as the Queen is concerned, it is likely that in the 1950s she came primarily into contact with similar U-RP speakers such as her prime ministers Anthony Eden, Harold Macmillan, Alec Douglas-Home.

'From the 1960s onwards, it is quite possible that the Queen came into contact with many more middle class and/or non-aristocratic speakers.'

He added that many prime ministers from the 1960s - such as James Callaghan, Margaret Thatcher, Harold Wilson, John Major and Tony Blair - are not upper-class RP speakers.

According to Professor Harrington's analysis, there have three main changes in the Queen's accent since the 1950s.

First, the 'a' in words like 'hat' or 'happy' have changed from sounding more like an 'e' to more like a present day 'a' sound.

For example in the 1957 broadcast she says 'thet men' but by the 1980s it has become 'that'.

Second, the 'u' in words like soon sounded more like the French 'u' in 'tout' where it is produced towards the back of the mouth but is now produced further forward in the mouth.

Finally the vowel in words ending in a 'y' like very, happy, really and family, were shorter and sounded like a short 'e' sound. 

In more recent broadcasts it has become longer more like the vowels said in 'feed'. 

According to the BBC, the changes in the Queen's accent have been reflected in other speakers of Received Pronunciation. 

Rather than using a diphthong – a combination of two vowel sounds – to say words like poor and moor, they now pronounce them in a way approaching maw and paw.

The Ys at the end of words have also become longer and less clipped than they may have been in the past.

Professor Harrington said: 'There are now those who speak a more modern form that verges on 'estuary' English, which is a mixture of RP and cockney.'