"One has to put up with the crude English method of development, of course."
Prime Ministers of the United Kingdom of Great Britain and Northern Ireland
1937-1940: Neville Chamberlain (Conservative)
1940-1942: Winston Churchill (Conservative) [1]
1942-1945: Stafford Cripps [2]
1945-1947: Herbert Morrison (Labour) [3]
1947-1950: Anthony Eden (Conservative) [4]
1950-1952: Stafford Cripps (Socialist Unity)
1952-????: Jennie Lee (Socialist Unity)
[1] Francis Drake had once said that those who have experienced shipwreck shudder even at a calm sea. Churchill had proven himself to be a stopped clock when it came to his denouncing of the interwar appeasement and that vindication alongside his previous War Cabinet record had made him the only real contender to replace Neville Chamberlain. Despite the initial doubts about the competence of the man responsible for the Gold Standard and Gallipoli, Churchill seemed to vindicate himself once more as he captured the public mood following the collapse of France; resigning the country to going on to the end, whatever the cost.
The problem was that the end didn't seem anymore within reach in 1942 than it did in 1940. The entry of the United States into the war had initially brought a sense of deliverance but this had shortly delivered more problems than it had solutions. The lack of American preparedness for the U-Boat threat had led to a 'Second Happy Time' which saw shipping losses soar and imports drop to their lowest level since the war. Meanwhile the Japanese swept throughout South East Asia like an unstoppable typhoon, humbling the British fleet whilst British colonies fell like dominoes. In North Africa June had started with the seemingly impregnable fortress of Tobruk falling to the Axis, it was an embarrasment Churchill had put a lot of stake in avoiding. Just like the fall of Singapore in February, his image was shaken and though he had gotten Britain through the worst it became an increasingly common opinion that another man would be needed to finish the job.
Churchill's badly handled attempt to flush out his rivals by holding a motion of confidence in his government led to his dismissal by Parliament but for all it is regarded as a disastrous misstep on his part he did reveal that his opponents hadn't quite figured out the personality needed. Many names were floated in earnest; Attlee, Beaverbrook, Bevin, Eden, but all were tangled up in the sort of political wrangling that should have occurred before the vote, had Churchill not called their bluff before they were ready. In haste it is decided that only a man of independent mind will do, and there happens to be one such figure. The British voice from the one part of the world where the Axis are being made to bleed.
[2] The decision to send a Christian Marxist to the palace to replace Churchill might have seemed to be a jarring transistion but Cripps' peculiarity was the main reason for finding himself where he was. Having been thrown out of the Labour party amidst his calls for the Comintern's Popular Front strategy to be applied to the UK, but personally hesitant to actually join the CPGB, Cripps found himself with no true political home by the time 1940 rolled around and his sympathies became an asset.
Facing off the German threat alone Britain found it necessary to try and improve the dreadful state of Anglo-Soviet relations and though Cripps initially made little headway in this regard he would become the leading architect of the Anti-Hitler alliance in the wake of Operation Barbarossa. Guarded support for the Soviet war effort amongst the British establishment was overshadowed by outright enthusiasm for the common cause amongst large sections of the working class and when Cripps returns to his Bristol constituency to announce that the Red Army will only defeat Hitler with the full participation of the British people his words are greeted by widespread acclaim. His warnings about a lack of urgency in the British war effort, unitentionally or not, are seen as a challenge to the current regime. When Churchill departs there is only one man beyond party interest whom the public will accept as his replacement.
Entering Downing Street, Cripps makes it clear that his agenda hasn't departed from his Bristol speech. There will be a Second Front as soon as possible. The Americans, previously sceptical of Cripps' political leanings are happy to see that Churchill's replacement is in favour of a landing in northern France in 1943. In the meantime Cripps, with support of the Soviets, manages to get the INC and the Raj to grudgingly accept immediate dominion status in exchange for post-war independence. It's a messy compromise but it helps to dampen the allure of Bose somewhat. This is also a hard sell to the Tory dominated Commons but the joint blows the WAllies score against the Axis in Egypt and French North Africa, overshadowed only by the Soviet victory at Stalingrad, help soften it. Cripps appears to be doing well and the focus returns to winning the war.
Luckily the weather is cooperative in allowing D-Day to be coordinated with the beginning of Operation Citadel and though the Germans abandon their Eastern Front gamble the Soviet counter-offensive prevents significant German forces from being sent to France. Normandy is a bloodbath all the same until the subsequent landings in Southern France break the deadlock in the WAllies favour. The Italians see the writing on the wall and switch sides followed by the Bulgarians, Finns and Romanians. The Germans occupy Hungary and knuckle down but by the end of 1943 it's clear the writing is on the wall.
The fighting on the actual West Wall is almost as bad as Normandy but by the time the Union Jack has been raised over the Reichstag it is hard for anyone to disagree that Cripps has taken Britain from being a spectator in the anti-fascist crusade to an active participant. Thailand switches sides as the Anglo-Indian army marches through Burma but the Japanese muddle on regardless. They are hardened by battle and wary of any potential promises made by their foe, they are resigned to fighting to the last no matter the cost. The same can also be said about the struggle for the Labour leadership that comes about in 1944.
Clement Attlee has served as a fine number two, first to Churchill and then to Cripps, but he's increasingly ill. He had only ever been meant to be a stop-gap for a more effective leader to arise and with the war nearly over an election looms. Some say that such a figure has obviously arisen in Cripps but the unions are dead against it. Bevin especially believes Cripps' Communist sympathies make him too dangerous to be welcomed back into the party, let alone lead it. Cripps is eager to try all the same, buoyed by the surprise success of an unofficial pro-Cripps candidate in the 1943 Bristol Central by-election. Germany has been defeated by the time of Labour conference but Bevin has found an ally in Herbert Morrison and the two successfully block Cripps' attempts to replace Attlee in favour of Morrison himself. Cripps is able to take a lot of Labour MPs with him however and by the time the Japanese surrender in the Spring of 1945 he has managed just about to string together a 'Win The Peace' coupon consisting of pro-Cripps Labour MPs, the Common Wealth Party, the ILP, and, of course, the CPGB. Their leader is the most popular man in Britain and they go into the 1945 election with a great deal of confidence.
[3] Cripps won the war but he can't herd cats and the disparate elements of his coalition make campaigning a nightmare, particularly when their most effective asset is too busy shaping a post-war global order to do as many public appearances as he would like. Morrison on the other hand has a credible agenda, it doesn't go as far as some might like but it's coherent programme for a better country as averse to the years of Tory failure or whatever 'Win The Peace' is supposed to be arguing for on any given day. In spite of the fears Cripps might do to Labour what Lloyd George did to the Liberals in 1918 the election ultimately delivers a slim Labour majority. The 'Win The Peace' coupon is widely seen as having underperformed although given the circumstances they likely did as well as could be expected in coming third. Freed from his commitments as PM Cripps has the freedom to hammer some order into his parliamentary grouping whilst the responsibility for Britain's role in the post-war world falls to Morrison.
Morrison was keen to become PM but the task ahead of him is daunting, only mildly better than that which faced his predecessors in 1942 or 1940. Britain is financially broken and India, finally able to flex the full extent of its dominion status, is swift with a UDI. The Soviets are suspected of being behind this and their shenanigans in Eastern Europe aren't exactly putting anyone's minds at ease. All the same the Americans aren't forthcoming with much help, they agree to bail out Britain but not without interest and a fundamental shift in the financial order of the western world in favour of themselves. The assassination of Badoglio and the subsequent red uprisings in northern Italy kickstart the Cold War and its one Morrison is happy to fight at the expense of the domestic agenda he was elected to carry out. Shoring up Britain's fading empire on the world stage isn't what the British people want however, rationing has only gotten worse since the end of Lend Lease and many are still homeless from the Blitz. These are often the first to fade into the snow during the famine of 1947.
[4] By the time the worst winter in living memory finally gives way to Spring Morrison's small majority has eroded to nothing and the Tories are able to force a general election with the support of the newly annointed Socialist Unity Party, who have finally gotten their act together. The result is the sort of split in the left-wing vote that was predicted in 1945 and although Cripps comes out of it better than Morrison, Anthony Eden is the main beneficiary albeit his majority isn't much healthier than Morrison's was.
Eden rose to prominence as a critic of appeasement and as wartime foreign minister was the obvious replacement for Churchill as Tory leader and, he though, Prime Minister. Eden brings Churchill into his cabinet but maintains that his focus will be on the dire domestic situation rather than foreign adventures. Eden has a high regard for Cripps personally but the SUP terrifies him, particularly now that they're His Majesty's Loyal Opposition. He will do anything to keep them out of power and that means maintaining a domestic focus. Britons might have a sentimentality for the empire but few can actually name any specific colonies, especially now that the Indians have stopped answering the phone. Korea might as well be a colony for all anyone would know. Of course it isn't, but Kim Il Sung thinks it is, and with Britain retreating inwards and the Americans focused on Italy and Greece he is given the green light from Stalin to unite Korea under Pyongyang.
Eden realises he can't backtrack on his electoral promises, particularly as he's starting to make headway on housebuilding and health insurance and so puts the call of the United Nations to defend South Korea to another ballot. He might not be as popular as Cripps but if he can frame the election as a choice between Communism and Democracy he's confident he can pull through.
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Special thanks to
@Comisario for his help with this.