In 2035, Vault-tec created a secretive UK arm called The KeepSafe Company. Keepsafe's mission was to purchase 30 sites across the British Isles so that they could build vaults in the UK. The Bunkers as they came to be known were basically the same as the US vaults: enormous self-contained underground techno caverns, each the size of a small town. Their vetting procedure for future Bunker citizens though was simple: enough money = entry, with a few pretty-ish poor people to be used as 'genetic diversity' as well as manual labour. The social experiments that pervaded their American operations were not going to be employed in England, as they viewed the little island nation as a handy cash cow where they would fleece the rich neckless elite for everything they could.
In the 1960s, underneath Poundbury Hillfort in Dorset, if you knew what to look for, was a Royal Observer corps monitoring post. As global politics shifted, it was eventually deemed unnecessary. In the early 1990s it was closed, sealed shut and was generally forgotten until Keepsafe went on the hunt for sites. In 2050, the run down historic site was bought up by Keepsafe's entirely above-board and not-at-all shadowy legal department and subsequently transformed into Bunker 26. This would house the second and third home-owning residents of the nearby New Poundbury, who would access it via an entrance disguised as a large garage.
Vault-Tec wasn't the only technological tendril to cross the Atlantic, West Tek's Power Armour was shipped over as well: under a government contract, variants were built in the UK under licence by the possibly corrupt Chomondley-TechnoTech. Under their moustachioed guidance, the T-45 became the Bedevere, the T-51 was renamed the Gawain, and the T-60 was knighted the Galahad
Using knowledge gained, Chomondley-TechnoTech started to create their own designs: The prototype was a highly modified T-45b dubbed The Loxley. The second design was more original, though it vaguely resembled the T-51 and was named the LittleJohn. Under the cover of a secret project in a facility hidden under the little peninsula called Portland, they created the third of their own designs: the sleek and scary-looking looking Lionheart. Plans for a fourth, "Project Gisbourne" were put on hold when in October of 2077 the Great War took place.
In 2055, Chomondley-TechnoTech realised that while their facilities on Portland were good for science and research, they were somewhat lousy for security when a bunch of stoner local kids were found smoking various narcotics in a disused basement. After a high-level meeting, the region boss made the decision to both boost security, and to shift actual production of armour units to a shiny new facility in Dorchester. Situated on the site of the old Marabout Industrial Estate, it seemed a natural move to get involved in the building of Bunker 26 and use part of it for storage and if they could get away with it, power too as the bunker powerplants were easily more than enough to supply the bunker alone. So, after a number of high-level meetings and the odd bribe, in a part of the underground citadel that wasn't on any of its general plans was an enormous storage and maintenance facility for power armour, connecting directly to the above ground manufacturing plant.
All this was played out against a backdrop of war: Oil was becoming scarce and prices were going through the roof. In 2052 with the economies of many countries suffering, with many going broke because of it, the European Commonwealth responded to the Middle East's price rises with violence. The UK's Queen Wendy the 1st voiced her displeasure at the necessity for war, but conceded that it was vital for the good of the commonwealth that they had the oil they required. She directed her government to draft in Chomondley-TechnoTech and their power armours to assist the Commonwealth. After initial resistance, Chomondley very reluctantly handed their designs for the Loxley to a competitor in France, Génie Technique. The French company quickly got to grips with their new mission and were churning out power armours for all they were worth.
The Resource War as it came to be known, spurred Keepsafe to seriously speed up their Bunker project and by 2058 all bunkers were complete, including the secret one reserved for the Keepsafe bosses and their families. The second that the Bunkers were complete, the locals that could went straight there, like rats up a drain pipe. This was a pretty wise move as it happened, as the Resource War was hotting-up big time. We may well have been sending troops and violence to the Middle East, but they were just as forthcoming in sending viciousness back in return. A lot of the Commonwealth suffered bombings and strikes and by the time the war came to an abrupt "Oh heck, we've actually un out of oil" halt in 2060 not many places in Europe or the Middle East were left unscathed. There was more to come though as the ancient distrusts that already lurked within the Commonwealth plus the general lack of oil caused tensions to boil over here, there and everywhere: mini wars started over the most minor of things. Some countries withdrew from the European bloc, while others tried to act like staying was still the best thing to do. The people in the Bunkers were altogether glad of their new homes, as all this chaos was becoming seriously dangerous.
The real test of their design came in the October of 2077, when China and the USA took aggression to a whole new level and destroyed each other. The rest of the world, not wanting to be left out, joined in the insanity as well and within a day the whole world was pretty much ruined. The Bunkers were sealed automatically on the detection of the launches, and hopefully Keepsafe had done their job properly and not skimped or cut corners when they created the huge crypts.
In 2062, France effectively imploded and separated. Infighting and enormous arguments split its government and divisions that had always been present within the country's political makeup turned into whopping great fracture lines. As a result, a large portion of Normandy seceded from France and declared itself to be the Kingdom of Cherbourg, ruled by the fairly self-absorbed and somewhat horrid King Claude Leveret the First. A coup in 2070 led by gruff military man and startlingly humourless twerp Albert Poulet resulted in Leveret being publicly executed and Poulet taking the crown. Poulet ruled with an iron power-fist and felt that the more weaponry you had at your disposal, the more power you had. With that in mind, after carefully researching their neighbours across the channel, in 2076 an invasion force left the kingdom of Cherbourg with the intention of attacking Chomondley-Technotech's Dorchester facility and taking all the power armour they could back home. They got as far as Castle Park in Dorchester when they ran smack into the 21st Royal defence force, a very dangerous, highly trained armoured division who were not about to let a load of high-grade military hardware get stolen by a self-titled mock-royal nerk. They had gotten wind of his intentions via a very clever surveillance network and decided that letting his forces get within a hair of their goal before embarrassing him as decisively as they could by placing an awful lot of their best people and hardware in his way. Poulet's invasion force was taken completely by surprise, and reeled under a sudden onslaught. They rallied fairly well and managed to put up quite a fight but in the end were no match for the 21st RDF. The remaining attackers were driven off and pursued all the way back to the coast, being subjected to random pot-shots by the victorious defenders.
Dorchester was certainly not unscathed and Castle Park was wrecked. Many houses were destroyed and quite a lot of interesting equipment remained, equipment which the Chomondley-Technotech research boys snaffled as quickly as they could before anyone else got it. It didn't really help though as then following year, the entire world was completely ruined.