Queen Elizabeth II becomes longest reigning monarch in the UK

Queen Elizabeth II is set to become Britain's longest-reigning monarch later when she passes the record set by her great-great-grandmother Queen Victoria who reigned between 1837 and 1901.

The BBC reports that 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.

The Queen, 89, will spend the day on official duties in Scotland and 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.

Prime Minister David Cameron will lead tributes in the House of Commons and there will be a salute on the River Thames where a flotilla of historic vessels, leisure cruisers and passenger boats will take part in a procession between Tower Bridge and the Houses of Parliament. The bridge will lift as a sign of respect and HMS Belfast will sound a four-gun salute, while the BT Tower in central London will scroll the message "Long may she reign".

Business in the House of Commons will be postponed for half an hour so MPs can pay tribute to the Queen.

Cameron paid tribute to the Queen at a cabinet meeting on Monday, saying she had a "remarkable record" and was "a symbol of Britain's enduring spirit admired around the world", the BBC reports.