I recently finished reading
Safe Passage. While I have some issues with this book, it's mainly a fairly solid piece of work. Two interesting alternate histories came to mind while I read the book.
A) They mentioned that Britain was more harmed by bad strategic thinking after the
Washington Naval Treaty than by the treaty itself.
B) Churchill worked to join the UK and the USA together so closely that full citizenship in both nations for all citizens was seriously being worked on. The simple fact that the USA rejected Empire and imperialism caused the idea to be shelved.
The first idea fits any "Lion Alone" scenario for WWII nicely. British admirals totally rejected giving aircraft carriers and submarines a central role in the British Navy. Battleships were becoming obsolete in many ways, especially if your navy lacked submarines and aircraft carriers to defend your battleships, and by overspending on battleships at the expense of other types of ships the navy seriously weakened Britain. If you find a way to bring Churchill, always a technology enthusiast, back as Lord of the Admiralty, then a more modern and flexible British Navy would alter several early battles.
Added bonus points, when FDR offered ahead of WWII to give Britain funds to fortify its Pacific base, it might had been wise for Britain to take the money. Had Singapore been properly fortified, it would have held out far longer. Yes the Washington Navy Treaty (see above) forbade fortifications, but the Japanese repudiated the Treaty long before FDR offered the money.
Centrum would certainly not like Churchill or FDR but a better WWII might keep the British Empire for a longer time.
Neither Churchill nor modern European Leftists ever get the simple fact that once the American people tried Imperialism in the late 19th and early 20th centuries, they found they didn't like it. Churchill's government and the USA were all for joining the USA and the UK as one nation, at least in many ways. But the USA just wouldn't accept the British Empire. The price for America joining up with Britain was that most of the Empire would become independent nations and the rest would become full equal parts of either Britain, Canada, Australia, New Zealand, or the USA. Basically America was willing to join a federated British union, but they wouldn't be imperialists.
Churchill always blamed Irish-Americans and racist Southern Whites for the refusal as he always saw the British Empire as a force for justice and especially racial justice. The European Left would simply reject the idea that any of this was serious if they'd even allow that it happened. Britain simply invested to much of its self-image in the Empire.
Centrum, faced with nut job Nazis and Stalinists, might still prefer a Union of the English Speaking Peoples. Getting around America's rejection of imperialism would be a major task.