The Queen has decided that, to commemorate her Diamond Jubilee, she will revert to her natural speaking style for the day on June 4th. Although she usually affects a very precise BBC English accent, coming from the west end of London means she naturally speaks with a typical London accent. And why not - the Queen is after all a Cockney.
Although Bruton Street, where the Queen was born is not often thought of as being a Cockney area, it falls within the part of London designated for defining a Cockney - someone born within earshot of Bow Bells. St Mary-Le-Bow church, rather than being in Bow is actually in Bow Lane in the City, and in 2000 a study determined that the bells could be heard up to four miles to the west, an area covering Mayfair.
So the Queen will spend the day speaking in a manner usually associated with the rough and ready working people of London and the cast of East-Enders. She is expected to capitalise on the one chance she has of letting her hair down by throwing in some rhyming slang and other Cockney phrases. She will probably make good use of these when she attends the Diamond Jubilee Concert at Buckingham Palace, ("Ow Gould blimey, Jessie J you berk, sing us anuver ding-dong!") and when she goes to light the Jubilee National Beacon ("Oos got a box of lucifers then - I've only gone un left mine in me uver rahnd-the-'ahses!").