This office was the used by the Prime Minister of the United Kingdom during his term in office. He met with two Ministers for Magic—Cornelius Fudge and Rufus Scrimgeour—in his office throughout the course of his time in control of the country.
The office of the Prime Minister of the United Kingdom was considered to be a tasteful room, with a white marble fireplace and long sash windows. The Prime Minister had a desk in the office, with a chair on one side for his own personal use, and at least two chairs on the other side for visitors. A telephone rested on the desk, and the Prime Minister kept a supply of whiskey in the office. In one corner of the room was a small oil painting of a man in a silver wig. The portrait was used by the British Ministry of Magic to communicate with the Muggle Prime Minister when the need arose. In addition, the fireplace in the office was connected to the Floo Network, allowing the current Minister for Magic to travel to the office.
Cornelius Fudge, Minister for Magic from 1990 to 1996, met two Prime Ministers in the office. Upon meeting the first individual, he revealed the existence of the Wizarding world to him. The Prime Minister believed Fudge to be a hoax, a trick played on him by the opposing political party and promptly attempted to throw Fudge out of the office's window.
When a new Prime Minister was elected, Fudge travelled to the office to introduce himself and reveal the existence of the Wizarding World. Despite Fudge's claim that they would probably never meet again after their first introduction since he would only need to meet the Prime Minister if incidents threatened the Muggle world, the Minister for Magic met the Prime Minister again in 1993 to inform him of Sirius Black's breakout from Azkaban. Convinced Black would be caught quickly, Fudge alerted the Prime Minister of the situation, and asked that the Muggles keep an eye out for Black, as well. It was during this meeting that Fudge filled the Prime Minister in on recent events in the Wizarding World, including the rise and fall of Lord Voldemort.
The next year, Fudge met again with the Prime Minister, to inform him of the riot that had taken place at the Quidditch World Cup, and that magical creatures were being brought into the country for the Triwizard Tournament, which was to be held at Hogwarts School of Witchcraft and Wizardry that year.
In 1996, the Prime Minister was under pressure after the collapse of the Brockdale Bridge, and a hurricane that had devastated parts of the South-West of England. Fudge again met with the Prime Minister, and informed him that Lord Voldemort had returned, and that he and his Death Eaters were responsible for both events, as well as the murders of Amelia Bones and Emmeline Vance, two gruesome murders that had made the Muggle newspapers. During the meeting, the Prime Minister learned that his new secretary, Kingsley Shacklebolt, was a highly skilled Auror and was charged with his protection. In addition, Fudge revealed that he had been sacked three days previously, and introduced the Prime Minister to the new Minister for Magic, Rufus Scrimgeour.
- Harry Potter and the Half-Blood Prince (First appearance)