Britain's Golden Age

Britain's Golden Age was the term given to the era under which Harriet Jones served as Prime Minister of Britain. Though the name suggested a peaceful era for Britain, it was actually a period of much conflict. The term was first used by the Ninth Doctor after Jones took charge of the aftermath of a world crisis, following a hostile takeover from the Slitheen family. (TV: World War Three) The Doctor had high hopes for Harriet's term, but when he discovered a dark side to her rule in his tenth incarnation, he acted swiftly to get her removed from power, aborting the era before it came to pass. (TV: The Christmas Invasion)

History
Harriet Jones became Prime Minister in 2006. During Harriet Jones's rule, Britain became more involved in the defence against alien attacks due to Jones's views and fears towards the damage they could inflict on human society.

Britain's Golden Age was marked by several initiatives to keep the public safe from these potential attacks. There were also attempts to outreach to alien life to see if there were aliens willing to befriend Earth, which would dispel the fears humans had towards extraterrestrials. When the first significant outreach was met with an act of violence and invasion from another alien race, the Sycorax, Harriet submitted to her belief that Earth had to be defended from all aliens, resorting to deadly measures to keep it out of their hands; on Christmas Day 2006, she ordered Torchwood One to open fire on the Sycorax, killing the ship before it could contact anyone else. The Doctor responded with extreme fury, calling it a genocide. Disgusted, he chose to stop her rule immediately by instilling the notion that she was tired into her aide, Alex Klein. This trickled down to affect her standing with the public and various other authority figures, which increased her paranoia and led them to think she was growing ill. (TV: The Christmas Invasion) Replaced by no later than 2008 with the election of, the Doctor effectively erased the notion of Jones' rule becoming a "golden age" from history. (TV: The Sound of Drums)

Use in alternate universes
The Pete Tyler of an alternate universe once mentioned that his world's counterpart to Jones also ruled under a golden age. However, the Torchwood One of that universe had been caught by the government for its nefarious activity and was re-purposed to operate within ethical standards, indicating the Jones of this universe had a cleaner rule.