The secret recipe is back in the safe for another year, and the dust sheets have gone back over the machinery: the Queen's Christmas chocolate is ready and has been dispatched to Buckingham Palace. It is, as the red label boasts, truly a "superior" chocolate.

Cadbury uses a special machine and a special recipe at the Bournville factory, it has emerged, solely to make batches of gold foil-wrapped dark chocolate just for the royal household, delivered in small boxloads direct to Buckingham Palace, Windsor Castle and Sandringham.

Although labelled Culinary Plain Chocolate, its unusually high cocoa solids content apparently makes it suitable for either cooking or tucking into while watching the Queen's speech.

A company spokesman said: "We do make the Queen a bar of dark chocolate. It's not for sale to the public. We've been providing chocolates to the royal family since Victorian times, but I cannot discuss the recipe."

The Mail media group, which has mounted a campaign against the giant American Kraft food company's attempt to take over the chocolate firm, solemnly warned: "If it is taken over, there is no guarantee Cadbury would continue to make the Queen's chocolate."