A new official photograph has been released to mark the occasion

Queen Elizabeth II becomes Britain’s longest-reigning monarch later when she passes the record set by her great-great-grandmother Queen Victoria.

The Queen will have reigned for 63 years and seven months – calculated at 23,226 days, 16 hours and approximately 30 minutes at about 17:30 BST.

Prime Minister David Cameron will lead tributes in the House of Commons and there will be a River Thames Salute. The Queen, who is 89, will spend the day on official duties in Scotland.

The exact moment the Queen reaches the milestone is not known because her father, George VI, passed away in the early hours of 6 February 1952. Business in the Commons will be postponed for half an hour so MPs can pay tribute to the Queen.

It will be day 23,226 of her reign. The Queen is determined that it should in no way be exceptional. She has let it be known with some emphasis that she does not want a fuss to be made. Buckingham Palace has released an official photograph to mark the occasion, taken by Mary McCartney in the Queen’s private audience room. (BBC)