Princesses Elizabeth and Margaret, the future Queen Elizabeth II and Margaret, Countess of Snowden respectively, did actually join the crowds in London to celebrate VE Day on May 8, 1945. However, instead of having one officer each as a chaperone, they were joined by a group of Guards officers who were their friends. In her diary, Elizabeth wrote: "Trafalgar Square, Piccadilly, Pall Mall, walked simply miles. Saw parents on balcony at 12.30am - ate, partied, bed 3am!".
The army jazz band featured during the Chelsea Barracks scene were actually members of the Echo 42 Jazz Band drafted in to be realistic extras.
The George pub used for various scenes is in The Land of Green Ginger in Hull and claims to have the smallest window in the world. This is basically a gap in between two wall stones that has been glazed. Apparently, in the old days, a boy would sit in the hollow wall and identify genuine hotel guests by looking through the window. He would then let them in by opening the courtyard gate. The window is about 1in by 10in
The film takes place on May 8, 1945. The Trafalgar Square scene was filmed on 8th May 2014, the 69th anniversary of VE night.
In this film, Roger Allam plays a bootlegger that helped Princess Margaret. In La reina (2006), he played Robin Janvrin, who was the assistant to Princess Margaret's sister, Queen Elizabeth.