The “Inferno” deep mantle drilling disaster shot a lance of hot plasma beyond the upper edge of the atmosphere, with an explosive concussion that was heard as far as Paris and shattered most windows in London, some 50 miles from Eastchester (our Colchester). Fortunately, the pocket of Stahlman’s gas into which the drilling operation had broken into was a small and isolated one, and its release from its normal pressurized condition failed to start a sub-crustal chain reaction, an event which could have returned the entire planet to its primordial, molten state. As it was, the results were still a disaster on a global scale: some 300 square miles of English countryside were reduced to a lake of bubbling lava, so much debris was kicked into the atmosphere that the world suffered a “year without summer” which led to extensive famine in the poorer parts of the globe and led to revolution in India, and the formation of a colossal lava reservoir deep in the crust beneath England destabilized the west Eurasian crustal plate to the extent that in 1999 earthquakes are almost as characteristic of Europe as of OTL California: according to some geologists, the crustal plate may be splitting slowly on a west-east axis passing under England, a view supported by the emergence of a ferociously active volcanic new island in the North Sea. Increasing volcanic effects and tectonic activity have been noted as far away as the Pacific Ring of Fire.
More locally, in England the damage created by the eruption was compounded by a rain of lava-hot green goo, consisting of a primordial form of life long extinct on the cooling outer shell of the planet: it proved infectious, causing humans to regress on a cellular level, into shaggy, bestial (and green) men-monsters, which sought to infect others to become like themselves.  Terribly strong, radiating heat intense enough to carbonize(normal) human flesh, and almost unkillable by conventional hand arms, although vulnerable to cold, the “Primords” spread and multiplied, and were only stopped with heavy use of high explosives and the seizure of every CO2 fire extinguisher and canister liquid oxygen in southern England. (Gas didn’t work, and flamethrowers were quite counterproductive). Although the government under President John Smith reacted with its usual speed, efficiency, and brutality, in the end over two million British citizens perished, above and beyond the close to a million victims of the eruption itself, and half of London was burned down as a result of heat-loving Primords setting fires to keep warm. Italian and other troops from British allies were eventually brought in to help mop up, although, from the point of view of those who lost family and friends to the Primords, the government had waited inexcusably long before asking for help. (Not that anyone said this aloud, at least outside very small circles of very trustworthy people. Criticizing the Republic’s leadership was an unhealthy occupation).
The eruption and its disastrous effects (aside from leading to rapid shutdown of Russia’s own mantle penetration project) led to a serious worldwide economic slump, which would last through the rest of the 1970s. President John Smith stepped down in 1976 and disappeared under somewhat mysterious circumstances – although official accounts have him enjoying his retirement in Malaysia, many suspect a quiet coup, something not particularly appeased by the largely unknown new President, William Abberton, a government scientist afflicted by bizarre rumors of vampirism, officially blamed on Australian propaganda.
(The next decade, of course, saw the Shadow War, as genetically engineered and cybernetically enhanced British vampires carried out a large-scale international program of terror, assassination and political destabilization against British competitors and enemies internal and external, not without successes, but also dangerously disrupting the unity of the Conclave and pushing Britain close to political isolation).
A few other events of interest:
1977-1990: the US pursues its own “super soldier” program through attempts to identify and recruit psychics, and enhance their powers by various means, with somewhat variable results.
1980: The destruction of several North Sea oil platforms is pinned on banned Scottish Nationslists, which of course copiously confess at their show trials. Very few people know about the relationship between these events and a violent explosion in an abandoned Welsh quarry, and even fewer know that (let alone why) a bomber carrying a 15 megaton device is kept constantly ready to take off in a secret hanger within a five minutes flight of Loch Ness.
1986: the destruction of planet Mondas by Conclave Z-bombs causes a radiation pulse that causes electromagnetic damage to power systems and computers worldwide, and the debris blown into space forms a menace that will threaten Earth with meteor impacts for the rest of the 20th century: however, the formation of the international Space Shield force to intercept and destroy threatening asteroids will create an internationalist force admired globally, and help heal some of the wounds caused by the Shadow war, even as a hidden struggle for control of Cybermen technology left at the South Pole rages behind closed doors.
1987: Prime Minister Abberton passes on under somewhat uncertain circumstances: it is a closed-casket funeral.
1992: the Two Chinas reunite.
1996: a Chinese high-tech haunted house meant to take place in the Gold Coast Festival is shut down in early testing due to overly aggressive robots: Chinese repairmen arrive to find the place mysteriously wrecked in spite of undisturbed locked doors, and a couple very odd looking trashed machines with rotting organic residue inside. The Chinese secret service manages to smuggle them out of the country before the British security forces cotton on.
1999: a peculiar radar “black spot” is located above Canary Warf.
As of 1999, on the eve of a new millennium (although some wiseasses point out that it won’t arrive till the end of 2000), the Conclave has been drawn into closer agreement than ever before by the increasing evidence that the universe is a seriously dangerous place. Plots are being drawn behind the scenes to create a single overarching governing body for the American, British, Russian and Japanese blocks (the Chinese are still being a bit difficult); it won’t be quite a world government, but once formed it will have the power needed to bring the rest of the globe in line. To survive, humanity must be unified, and expand to the stars.
Russia has risen in the relative power rankings: the Chinese, even more so, eroding Japanese dominance of the Greater East Asian Co-Prosperity Sphere, which is nowadays essentially split into Chinese and Japanese factions.
Technology is, thanks to stolen alien tech, quite advanced. Cybernetics are highly developed, with cyborgs human and otherwise, regenerating-metal robot soldiers (and nanotech weapons to rust them into scrap), and whole-heartedly fascist sapient computers. (The Scandinavians are becoming disturbingly fascinated with cybernetic upgrades: a Swedish scientist reportedly has stated “we could do much, much better than the Cybermen.”)There are energy weapons that could carve CHA on the Moon, if anyone wanted to. Space travel has been greatly enhanced since the 1970s: there are now manned bases across the solar system, and faster than light travel is reported to be “right around the corner.”
An ancient, Fendahl-infected skull, indestructible by anything short of a supernova, lies shallowly buried below the debris from the explosion of a nuclear artillery shell, waiting patiently for a new puppet.
The wreckage of Mondas continues to speed into interstellar space.
The French continue to fiddle with Scaroth’s time technology, never perfected without the aid of Romana. Turning an egg into an adult chicken and then a skeleton is a good party trick, but it’s of limited utility.
The British have more functional time travel technology, although they still tend to suffer from unfortunate “dinosaurs pop up in the present” side effects. There are plans in effect to send people back in time and recreate Britain 5 million BC if it looks like curtains in the present, although scientists mutter about “catastrophic paradox” and “timeline implosion” where the morale officers can’t hear them.
Skaldak the Ice Warrior remains frozen in the Arctic ice.
 A handful of Primords were captured alive and kept in concrete-lined pits they could not climb out of: over a few years they continued to slowly degenerate, into misshapen fanged quadrupeds, then into crawling things, finally into horrors like immense green jellyfish slithering from place to place.