A major breach in royal protocol occurred when a senior member of the Royal Family marked their birthday, forcing Number 10 to apologise, newly released documents show. The files, opened at the National Archives in Kew, reveal that the private office of former Prime Minister John Major made a mistake when commemorating Queen Elizabeth, The Queen Mother's birthday.

The documents explain that Major's office was contacted directly by The Queen Mother’s private secretary after the message to mark her 94th birthday in 1994 arrived, using the incorrect form of address.

Captain Sir Alastair Aird telephoned Downing Street to request an explanation for what he described as an “improperly addressed” message.

The error prompted an internal investigation by the Prime Minister’s staff. Although the documents have just been released, the cause of the mistake remains undisclosed.

In a letter following the inquiry, Roderic Lyne from John Major’s office sent an apology and was at pains to distance Downing Street from having any responsibility for the error. He went on to suggest that it had happened during transmission rather than during the preparation of the annual message.

Mr Lyne wrote: “The message itself, as it left our hands, was entirely correct. However, in transmitting it, it appears that British Telecom most unfortunately addressed the telegram in the improper manner which you described.”

He added that Downing Street staff in were “sticklers for the correct form” and would never typically commit such a high-profile mistake.

Then, attempting to make light of the situation, Mr Lyne suggested a possible way to avoid similar embarrassments in future, quipping that telegrams were “in any case going out of fashion”.

Despite the major breach of protocol, the Queen Mother responded with her usual good manners and courtesy and sent the Prime Minister and his wife her own message to thank them for marking her special day. She wrote back: “I was very touched by your kind message of good wishes on my birthday and send you both my warm thanks."

The Queen Mother passed away at Royal Lodge in 2002 at the age of 101. The newly released files form part of a routine release of Government records after 20 years, although this is an unusual case as material concerning the Royal Family is often withheld under the Public Records Act.