I love this idea! One of the fun things about using a historic period as a campaign setting, is having various historical figures make cameos as npc's.
Each of those NPCs should have a Secret, an Ambition and at least one Plot.
You can set up their Plots to, like dungeonworld, have portents and results. Portents are the result of them advancing their plots (and give players a chance to see it in action), and results are the change to the world state if their plot succeeds.
Secrets are just fun.
You can make a table of such NPCs and their plots, and randomly roll to see which of them advance their Plots, then add the portents to the local news (plus some other random crap). A weekly newspaper! That would be awesome, where you can embed random noise plus plot advancement for your various NPC protagonists.
That is PERFECT! This is exactly the sort of system I was looking for. I hadn't even heard of it before. As I see it, Crowley will attempt to unlock the secret to immortality, and burn down parliament. Much like in the game, the campaign will steer towards this climactic finale where the party does battle with a super powered Crowley monster. But in order for him to get there, he needs to accomplish a few different goals. These threats are then linked to various response missions of the players.
Campaign Front.
Dangers:
Arcane Enemies: Crowley. Doom: Ascends to immortal monster form
Ambitious Organization: NAZIs. Doom: Coup, takes over government
Planar Forces: Demon Lord. Doom: Demonic infestation of England
Cursed Places: Tower of London. Doom: Area falls into the shadowfell
Grim Portents: (NAZI)
A newspaper controlled by the Fascists being everywhere.
The founding of the British Union of Fascists.
"Brownshirts" smash union strikes.
Parliament blown up, blamed on communists.
Grim Portents: (Crowley)
Flesh golem experiment successful, escapes into the city.
Steals Rosetta stone to decode ancient text
Jan 24 1925 partial Solar Eclipse goes total, doesn't end until someone stops it.
Grim Portents: (Demon Lord)
The Heir to the Throne kidnapped
Archbishop possessed, starts crusade against demons that actually causes backlash
Everyone in a part of the city just dies, their blood staining the Thames red
Grim Portents: (Tower of London)
Guards of the Royal Jewels go missing. Jewels ... seems ... ok.
The Ravens increase in numbers. Those who hurt them suffer horrible misfortune.
A storm cloud forms over the tower, and never goes away.
Crowley is behind a lot of this. He is using the NAZIs to get access to arcane materials held both by the British and overseas. The demon lord is providing power. And the tower is where he intends to ascend to immortality, crowning himself using the corrupted crown jewels as the immortal dark lord of the eternal British empire.
At the same time, the other Dangers are using Crowley. The actual doom is opposed or not really needed by the other dangers, except Crowley actually does want the Tower to fall into the Shadowfel.
Then adventure fronts! The above are major campaign events.