Inferno universe

Accessed via a power accident at the Inferno Project, the Third Doctor discovered a parallel universe where Great Britain was a republic governed by a fascist regime. Although some details were known about the history of this world, the Third Doctor personally experienced it only in the environs of its version of the Inferno Project. The Third Doctor described it as a "parallel space-time continuum" (TV: Inferno) whereas the Seventh Doctor called it an alternate timeline. (PROSE: Timewyrm: Revelation)

19th century
The Confederate States of America won the American Civil War during the 1860s. In the war's aftermath, the American Confederation was established. (PROSE: The Face of the Enemy)

20th century
Joseph Stalin was the leader of White Russia. (PROSE: The Face of the Enemy)

The British Royal Family were executed for undisclosed reasons in 1943. Brigade Leader Lethbridge-Stewart spoke about their deaths with relish. (TV: Inferno) The Japanese successfully built their Asian Co-Prosperity Sphere. The Second World War never happened since Europe was divided into allied British and Russian spheres of influence, which were able to intimidate Adolf Hitler into backing down from his sabre-rattling.

This world was effectively ruled by the Conclave, a parallel of the United Nations Security Council, made up of the five main continents. The Conclave were based at Copernicus moon base to protect the delegates from attack and to intimidate subversive groups and enemy nations such as Australia. The reasoning was since the Moon could be seen from all parts of the civilised world it would serve as a reminder that the Conclave was watching. By the 1970s, the main powers were Russia, India, the American Confederation, the Asian Co-Prosperity Sphere, and Britain (representing Europe). (PROSE: The Face of the Enemy)

The parallel of UNIT was known as the European Axis Military Corps (PROSE: Still Lives) and the British contingent of this organisation was known as the Republican Security Forces. In 1970, many of the members of the RSF were the parallels of British UNIT members, including Alistair Gordon Lethbridge-Stewart, Elizabeth Shaw and John Benton. In this universe, Shaw had never become a scientist and the Brigadier and Benton had grown up harsh and sadistic. (TV: Inferno) The RSF had been active since at least 1959, when they fought the Bannermen in Wales and reverse-engineered the alien's technology. (PROSE: The Face of the Enemy)

The Great Intelligence launched an attack on Britain in this timeline as well. Koschei, here having not become the Master, saved the world from the Intelligence but was then captured, tortured, and pumped for information for years by the Security Forces. (PROSE: The Face of the Enemy)

At some point, this universe's Doctor arrived on Earth. He took over the Republic of Great Britain and became its leader. (PROSE: Timewyrm: Revelation) He may have been responsible for some of the technological advances. (PROSE: The Face of the Enemy)

Shortly after the Doctor's unplanned arrival in this universe, an accident at Stahlman's project devastated the entire surface of the planet within thirty-nine hours. The only survivors were those in bunkers, space stations, or on the Moon. This world's Doctor was killed when the fallout from the disaster at Eastchester destroyed London. (TV: Inferno, PROSE: The Face of the Enemy)

The Doctor had recognised the President's face was one of the regenerations he could have chosen at the trial. He would be haunted afterwards by the knowledge of what his alternate self had done. (PROSE: Timewyrm: Revelation)

While the Doctor and Joe were visiting Peladon, the surviving leaders of this Earth started to cross over the Doctor's world. They planned to kill and replace their counterparts, but UNIT (reluctantly working with the Master) thwarted the plot. (PROSE: The Face of the Enemy)

Other information

 * When his conversation with his third incarnation's persona revealed the identity of the dictator of the Inferno Earth, the Seventh Doctor wondered if the Timewyrm had any part in creating this timeline as part of her efforts to weaken him. (PROSE: Timewyrm: Revelation)
 * Jane Page may have been a native of this timeline as she worked for the counter-espionage agency of a dictatorial British Republic. She was removed from her timeline by Gabriel and Tanith. (PROSE: Falls the Shadow)

Behind the scenes

 * The world is never actually referred to as "Inferno Earth" in any known DWU story. However it serves as a useful shorthand. It's a logical in-universe term, since the Doctor accessed that particular Earth at the Inferno Project — something the novelisation tells us is colloquially known as "the Inferno".