The Queen has worn a face mask in public for the first time as she made a poignant pilgrimage to the grave of the Unknown Warrior to mark the centenary of his burial.
The head of state followed Government regulations and adopted the covering when she visited the place of worship for a brief ceremony - her first public engagement in London since March.
A royal aide described the service as "deeply personal" for the monarch, who was married at the Abbey in November 1947, and in tribute to the symbolic serviceman she left flowers, based on her wedding bouquet, at his final resting place.
Members of the royal family from the Prince of Wales to the Duke and Duchess of Cambridge have appeared at official events wearing face coverings for the past few months, and the Queen has now followed suit.
Details about the black mask, which was edged with white, have not been released by Buckingham Palace but it is thought the covering was made by Angela Kelly, the Queen's personal adviser and curator, who designs many of her outfits.
After the service on Wednesday, Dr David Hoyle, the Dean of Westminster, said: "It was wonderful to see Her Majesty in such good spirits and good health.
"We talked about the centenary and the life of the Abbey. This is the place where she was married and she's conscious of those associations.
"This is a moment where the Abbey does its job as the national place of worship. The story of the unknown warrior touches us all. It's very hard for all churches to shut their doors, it goes against everything we are ordained to do, which is to gather people together.
"Like so many communities, we're divided and that's difficult. It is very special for Her Majesty to do this, given the current restrictions. I know, because people tell me, that these moments when Her Majesty is in the Abbey gives us a sense of renewed purpose and encouragement. It makes us feel very privileged."
The Queen was criticised for not wearing a face covering when in October she visited the Defence Science and Technology Laboratory at Porton Down with the Duke of Cambridge.
At the time, Graham Smith, chief executive of Republic, which campaigns for an elected head of state, said the Queen should have been "setting an example", while royal commentator Joe Little, managing editor of Majesty magazine, said medical advice would have been sought when planning the visit.
Face coverings are required by law in certain indoor settings such as on public transport, in shops and places of worship.
The Government recommends wearing a face covering in indoor places where social distancing may be difficult and where the public come into contact with those they do not normally meet.
Commemorations had been planned to mark the 100th anniversaries of the interment of the Unknown Warrior - who represents First World War dead whose place of death is not known, or whose remains are unidentified - and the unveiling of Cenotaph, both staged on November 11 1920.
But the Queen requested the service after the coronavirus pandemic forced much of the plans, which would have involved the royal family, to be scaled back, and the 94-year-old monarch, who spent the first lockdown shielding at Windsor Castle, was advised not to attend an Abbey service marking the warrior's centenary next week.
The Prince of Wales and Duchess of Cornwall will join the congregation to commemorate the 100th anniversary of the burial on November 11, Armistice Day.
A royal source said: "The grave of the unknown warrior is as relevant and poignant today as it was when Her Majesty's grandfather and father stood in the Abbey at its side 100 years ago. It holds enormous significance for the country and the royal family.
"The Queen was keen that the centenary was marked appropriately. A simple but deeply personal act reflecting a tradition started by her mother 97 years ago felt the right thing to do."
The Queen took the opportunity during her rare trip to London to visit Buckingham Palace, her official residence in the capital.
The brief service was an intimate event, attended by just the Dean and the Queen's Equerry, Lieutenant Colonel Nana Kofi Twumasi-Ankrah, after royal doctors advised limiting the numbers.
After the Queen touched her bouquet - which featured orchids and myrtle - the Equerry laid it on a corner of the grave, sited close to the Abbey's great west door, and after a prayer from the Dean the monarch bowed her head.
Pipe Major Richard Grisdale, the Queen's piper, positioned high in the Abbey's organ loft, played a lament, the Flowers of the Forest, as the Queen, dressed in black and wearing a poppy and the Jardine star brooch, was left in solemn reflection for a few moments.
The late Queen Mother established the tradition of royal brides sending their wedding bouquets to the Abbey to be placed on the grave of the Unknown Warrior.
Her posy was left at the grave in 1923 after her wedding to the Duke of York, later George VI, in memory of her brother Fergus, who was killed in 1915 during the global conflict.
The concept of the Grave of the Unknown Warrior was inspired by the Reverend David Railton, who had served as a chaplain on the Western Front during the First World War.
After the conflict he wrote to the then Dean of Westminster, Herbert Ryle, about his proposal which was later supported by King George V, and the Prime Minister David Lloyd George.
The body was chosen from four unknown British servicemen, exhumed from four battle areas, by Brigadier General Louis Wyatt, commander of British forces in France and Flanders, and transported back to Britain.
On November 11 1920, the coffin was draped with a union flag and taken on a gun carriage to the Cenotaph, where the Queen's grandfather George V placed a wreath upon it.
The King was present, with his son the future King George VI, as the warrior was buried at the Abbey, and dropped a handful of earth from France onto his coffin during the service.